in response to russel,
yes there are things that are much easier in AB but it goes both ways. one shot instructions are one good example that japaneese do way better. also in omron you can force any signal not just i/o, AND you can download comments for example.
similar goes for mitsubishi. btw. i was just helping someone read floating number on older Mitsubishi micro plc that didn't support floats. i consider that conversion rather basic, it's just bit manipulation after checking out format of floats on internet (i've never done this conversion before, i was just curious to try it out and it was straight forward). anyone calling himself programmer should produce working code in a jiffy (not everyone working with plcs is familiar with boolean operators, masks etc.). clearly swapping that controller with more recent unit (cost $400-$800) is one way to handle it but that's not always worth it (specially if you are just reading single number comming from some other device).
some things japanese have done very well (boolet proof hardware, no defects like from AB or Siemens), there are things that they improved a lot (manuals, web presence etc. Omron has much improved software that has everything but kitchen sink etc.) but they could do more:
Both still need to work on translations. For example to select or configure programming port on PC side, one has to use menu option called "Change PLC". Omron for example also has mess of data tables that are not even named properly or one cannot use them as named. for example CIO or D/DM or T/C etc. (you cannot enter address as "CIO1.00" or "I:1.00", it has to be "1.00") system flags are different on different controllers, datatables sometimes have gaps and they (used to) push BCD (wasted range).
Mitsubishi has nice hardware and powerfull instructions but they have been lagging with software updates - a lot. Current GX still looks very old, newer software is in use in Japan for some time now but for some reason they are slow to introduce the same thing to North America. One thing I don't like is project file - it is not one file, it is tree of folders and files. imagine MS excel file format that instead of single document uses folders and bunch of files. I just started looking into FX series controllers (micros) and noticed amazing limitation - whole application has to be in just one ladder. this is just horrible. i've seen this before on the A series but i didn't think this would still be an issue. on FX2N platform configuration of the ENET adapter uses few registers per connection. They support eight connection but settings for each are scaterred all over the D datatable. for example registers that configure first connection are in D1000 range, connection2 is in D2000 range etc. this is VERY ugly. proper way is to have dedicated system area for hardware setup (com port settings, ethernet settings etc.).
Despite all limitations both of them chug along pretty good and familiarizing doesn't require big time investment.