Actually IPSC does have a production division..the rules are little different and the difference between it and USPSA production would make a difference in some particular gun choices..
For USPSA production..since mag capacity is limited to 10...that eliminates one of the prime factors..capacity..
since it all is scored minor..that eliminates another factor..power..
one of the choice to make is caliber..some folks like shooting a downloaded .40..they say shooting the heavier 155-180 gr bullet at a 125-130 power factor is way soft..the price of brass is cheap too..but you gotta reload..
9mm..lots of cheap ammo sources..both over the counter..and brass is cheap if you reload..
ok assuming we pick 9mm:
now the guns...each has strong points and weak points..this will depend on you...
The Glock is popular and reliable..the G34 offers a long sight radius which is a good thing. it is easy to get a great trigger, either do it yourself or have someone do it..I had Charlie Vanek do a trigger on my G34 to 1.5#. Add a set of Dawson adjustable rear and F/O front..and it is a great package. downside..it has the narrowest mag to magwell opening..really have to look your reloads in. also fo some it has a funky grip angle, so pointability can be an issue.
SIG226ST..great sights, points well, easy to get a really trick trigger. Its a really heavy gun. I have friend that shoots for Team SIG and he is doing really well..having switched from his Para P18LDA.
Para P18LDA..its a 1911..so point well..good sights, trigger is pretty nice, but the reset is super long..you realy got to get your finger off. Also fat mags to narrow magwell.
CZ75/85..this can be set up to be pretty trick..the action needs some work out of the box, but can be made really nice..good sights are available, it points well. I have an CZ75 and a SP01 that have had really nice action jobs and had good sights put on them..so far really reliable and accurate with both handloads and factory ammo. the gun points really well, mags slip in on the reloads and the trigger reach is short enough that my little fingers fit just right.
Beretta 92..gun points well..pretty much the same as the others..can be set up to shoot well..really like the Elite2 version..the DA pull for me is really long and hard to get my short fingers on it.
Smith 5906 and the 5906PC..this is a cool looking gun..I have heard lots about it..but have yet to see or shoot one..Heard the action on these can be made really sweet.
Tanfoglio Sport Production..new kid on the block..only seen the photos..looks like good sights, big magwell, etc.
Springfield XD tactical..can be set up with really awesome triggers and sights. consistent trigger pull like the glock. easy to reload.
that would be my list of guns to look at for shooting USPSA production.
each is pretty well proven to be reliable, accurate and proven capable of winning.