Tim Kohlman , Oct 17, 2009; 03:42 a.m.
Lauren, are you asking about the lenses or the camera itself?
The Om-4ti is preferred because they are newer and also alot of the OM-4 's had a problem in the circuit that chewed through batteries. There are some minor differences in terms of features however it's not major. The Om-4ti had support for the F280 flash, titanium body and better weather sealing from memory.
This site might be helpful as it gives you a run down of the entire OM system. You can also compare the differences between camera bodies and versions.
A good majority of the OM Zuiko lenses are excellent. You are correct with what you say about the 55/1.2 whilst I haven't used it myself I've always heard good things about. The 50/1.4's are good for the price but I tend to prefer a hand-picked 50/1.8 MIJ as it's usually a better performer if you're not worried about the difference in max aperture. As far as the 50mm lenses on offer be sure to check out the 50/3.5 macro, it's my new favourite lens.