I have built both T-55's from ACE and PST.
ACE produces versions of vehicles that others dont have, yet, the plastic is soft, alot of flash and it will test your patience, but again, for uniqueness, its the only game in town.
On the PST side, the plastic is crisp, hardly any flash, really easy to build, but, its just a basic kit.
If you want, I have done this and so have others, mix & match both into one. For mine, I used the road wheels, upper hull from PST if I remember correctly. From ACE, I used the lower hull and turret, due to it having more detail than the PST. On the tracks, ACE's is better. But remember, any part you do use from ACE, thier will be cleanup. Once you have them in your hands, you will be able to decide for yourself which parts to use.
In the end, it came out pretty good.