This I would contend -- If a bike is going fast enough to lock it's tires, then ABS is a decent feature to have as your last-resort 'safety net'. There are also stats out there showing that ABS does significantly reduce risk, at least in real world applications (this doesn't mean the track, where minivans don't cut in front of you with half a second to react before impact). Personally I see ABS on bikes the same as seatbelts, airbags, and ABS in cars -- One day it will likely be standard equipment on pretty much everything (and like the above, will still be hotly debated even at that time).
With that said, to the OP, DO LEARN how to brake without relying on ABS if you do get it. The idea is to not lock the brakes if possible, however it is a good safety net if you do.
At the end of day, that is what the OP needs to do -- both are good bikes, so you should go with whichever one feels right and seems like the best choice to you. To me, that was the CBR250R, for others, it's the Ninja. Go sit on both, talk numbers with dealers, and then make your own decision, not the decision of anyone here on the forum.