To rail or not to rail, that is the question.
In my opinion this is more important than the block/no block issue because with my handy little guide here (CZ Tuning 101 with Professor Atlas) and some CGW parts you can get a great trigger with a block equipped gun. Most people like the rail because it shoots a hair softer, but the no rail models trade a little more muzzle flip for less weight. Keep in mind these are differences of a tiny degree, it's not like a Stock II vs Glock 17
You will most likely be happy with either, but if you favor the soft push of 147s over the snap of 124s I recommend the rail, be it the base SP01 or the SP01 Shadow Target.