Personally I can relate to atatari's dilemma in a sense. GE does do things uniquely and if using LM90 it can be difficult to troubleshoot, but any dos based software can be difficult in a sense. Poor graphics (actually none), small screen ( even if expanded may not see more than one rung at a time), requires using different screens for many minor details.
I am not in the league with most programmers here but with an XP machine, no serial port(using a USB adapter) and VersaPro I can still connect to GE 90-30 to store or load. Its possible to work with older firmware versions by turning off the warnings but I wouldnt advise it. For approximately $87 US you can buy the firmware upgrade and eliminate those issues.
Personally here is how I see it, if you are familiar with AB in depth and can rewrite the program then submit that to the powers that be and let them decide. Personally I think if you are that familiar with AB then it would be nothing to master GE. Again Preference plays an important part in all this. IF you have the software for AB or can talk the powers into obtaining it, the plc and I/O, and are more comfortable with it then you should go for it. I wouldnt expect the cost to be more than $10,000 US maybe with the software.
If the powers that be arent interested in spending that much then go for the VersaPro even if others say its obsolete (it may be but its still sold and supported so I am not sure where obsolescence applies). It is windows based and does work (at least for me it does) and the cost is way below what would be called for in replacing the unit with an SLC. Overall the GE Fanuc is a decent plc and not hard to deal with.
Sometimes our jobs mean we have to deal with things we arent comfortable with but in time you will learn and be the better for it.