As a caveat -
I am not an expert, and I shoot less than 2000 rounds a year through all my guns. In 9 mm, about half of that goes through a Glock 19 - I bought my first Glock 19 maybe 20 years ago, or more. Also, I am not trying to be inflammatory in any manner, but think that since I have been fortunate to have owned a lot of nice HiPowers, I would try to summarize some impressions.
I have always had a fascination for Browning HiPowers - I lover the way they fit my hand, and find them the most beautiful on handguns. That said, I like shoot a 1911 in 45 a bit more.
Over the years I got into custom HiPowers, and have owned full house customs by (using last names for simplicity, no disrespect meant)
Garthwaite
Wickman
Novaks (probably a Bonar gun)
Yost
EGW
Cylinder-Slide
I have seen many other custom guns by the above smiths, and also by Hoag. Additionally Don Williams did some great wrk for me.
All of the above smiths do great work, and probably the main difference is in overall impression. Also, my impression may not be yours.
Triggers
I have tried to compare triggers - and often tricked myself (go in the gun closet, in the dark, and swithch between two cocked guns). One thing in trying to compare is that I think if the same smith did 10 guns, there would be some difference in each gun, and that the standard deviation on the triggers would probably be as mush as 1/4 lb or more. Also, it seems that there is a percetual dif in the same trigger on the same gun - think how many times you need to dry fire two or three times to tell what you think of a trigger job.
The magazine safety can relly screw up atrigger, and removing it is not all that hard, if the trigger pivot pin comes out OK on your gun. That can be surprizingly hard to drive out, and if you try, be prepared that you might bugger the frame. Be sure to use a cupped roll pin. Also, on one full house gun the pin kept coming out, and I returned it I think twice because of that (stuff happens).
So, with regard to triggers - I suspect what variance I have is more perceptual. I have not tried a Yost short return next to a regular return.
Safety- extended
I like a high grip on all guns, but it is even more important for me on a HP. HP's tend to have muzzle jump (the 40 is much worse), and the high grip with some pressure on the safety makes a big difference. I am sure all of the Smiths will build up a safety for you, the EGW was the biggest of the ones I have had, and I liked it the best. Nothing wrong with the other, just my personal pref. Also, the EGW is a bit more square - made the gun a little more industrial. I think some would say it clashed with the overall aesthetics of a HiPower. The below picture is the EGW safety on a HiPower that was chopped by Cylinder and Slide:
This is a Cylinder-Slide gun, and thumb safety, see how it is very rounded:
Yost does his a little different, with a different symetry, and to me, it is somewhere between the two above:
http://yost-bonitz.com/bigphoto/package ... .jpg/large
I can not find any pictures of a Novak (which I am told is identical to Hoag's), but it is similiar to the Cylinder-Slide, maybe a bit smaller.
Hammers:
A stock hammer (ring or or not) on a stock gun will bite me. bobbing the hammer will work, and when I am using a HiGrip, it turns out the web of my hand sits a little lower behind the hammer. The C-S ring hammer has worked for me. All of the smiths will bob a hammer.
The hammer on this gun (a Pathfinder), was bobbed by Yost, and it was exactly right for me- Ted also fit the Spgels, and they were perfect:

I have never seen the hammer that Don Williams does but this picture is worth looking at:
http://www.theactionworks.com/Gallery/t ... fault.aspx
Grip treatments
I would take my calipers to gun shops, measuring the thickness of HiPower front straps. I finnally found a relatively plump practical model, that Gartwait checkered at 30 LPI for me. It was not all that grippy, I think he was uncomfortable going deep enough to make it sharp. I would love to hold the 40LPI that Yost does, I have a CCO that he did 40 LPI, and the stick to your hand is incredible. I can not tell much difference between all the stippling (and every gun except the Garthwaite and the EGW were stippled). My absolute favorite was the checkered insert from EGW.
I think this was 20 LPI, notice that the trigger area is cleared a bit (also seen on the Yost, or maybe that was the way the gun came?). I like grippy, but that was a bit too sharp, like holding golf cleats while someone walked on your hands - so I sent the gn back to have it dulled a bit, and the result was great.

At the same time, I found that the gun rocked a bit in my hand - there was slippage at the heal - so I asked something to be done there - picture is better than language:
Slide release-
If I was building from scrathc, I would try to find a bigger slide release. Take a look at the checkering on the Yost SRT in the above pictures, I think it is worthwhile.
Beavertail -
This is a matter of personal choice,
I know that the follwoing smiths do it:
Yost, Novaks, EGW, Cylinder-Slide, but others probably do also. There is a range from slender to more bulbous, each has pictures on their websites.
Barrels - I do think you get a little more accuracy from a Barsto, but it probably does not matter all that much.
The Cylinder-Slide Pathfinder:
I think it is a really neat package. You can save some money by having a FM detective top end used instead of cutting down your HiPower. I spoke with them on the phone about it, they were very impressed by my FM upper, and said the Rockwell hardness was harder than a typical Hipower. This gun got a trigger job, Novak sights and reliability package from Don Williams, then Cylinder-Slide cut down the frame, then EGW put the fiberoptic on the fron (or maybe Don did), and installed their safety, then I sent it for BlackT.
OK - my dream gun, if all the smiths would go long:
Start with a practical model,
Have EGW do the front strap insert, see if I can get them to checker the butt, if not then serate it, also the safety and beavertail, But i would ask them to make the beavertail about a 1/4 inch shorter. Then I would send it to Cylinder and Slide for their pathfinder package, limiting what they do to the cutting down, plus the installation of a Barsto Barrel. When it came back I would shoot it for a bit. It would probably then go to Yost for the hammer bob, checker the slide release and might as well do the mag release at the same time, and a short trigger job. Novak rear sight, serrated and matched the the back of the slide, fiberoptic front site. Install Nice Spegels. Flatter slide top and serrate. Polish the slide. The frame would probably go back to EGW for ETreat, but I might send it to BlackT (or might do the internals in BlackT). On the other hand, if there was a long delay I would be comfortable having Don williams do the above work or EGW, they just don't do the short trigger (or maybe they do and i don't know it, sorry to be insulting).
Books/videos
If you are going to mess with a HiPower, your ought to get Stephen Camps cards. The AGI video is so so, but the Graham one (Arizona Gun runners) is great! - and I will sell mine to you, when I find it.
Overall impression-
Proably the most cohesive and aesthetically pleasing package is the Yost SRT - the parts are very complimentary and there is some synergy between the lines.
The Novak and Cylinder-Slide packages are very straightforward improvements.
I think the EGW work is a bit more industrial (or at least the bits I chose).
Richard