both good guns. question is: are you the kind of mod freak? if so, the 34 and glocks at large are easy to modify, plenty of parts available. as for the CZ, yep you still can get some goodies for, but changes they brings will never get as dramatic (lol) as on glocks .
i've built myself couple limited 10 glocks(17,35,34 ) who are at light years to what they were before. trigger weight break (my 35 is at 2.3 onces break) , weight added-removed, slide lightened ....i've changed all internals to reach a feel only thousand dollars guns can provide.