I had the bad cramps that radiate down into my legs. And I agree, labor is a totally different sensation. It started out like bad cramps that I couldn't sleep through and then within the span of a few hours it had transformed into this sensation, almost like your midsection being in a vice grip, that I had to concentrate on breathing through so it didn't suck the air out of me. It's not that they were horrible, at least not until the last few hours out of the 20 I was in labor, but I just had to actively concentrate on staying on top of them. That being said, ds was born sunny side up so it also came with some wicked back labor and part of my cervical lip was stuck for awhile. I keep telling myself that the next one will be a little easier (I hope)! After pains for me were just like mild menstrual cramps.
ETA: I will say that at least during labor, you have the break in contractions whereas menstrual cramps are more constant. Well that was until my contractions were right on top of each other, it's not horrible when you do have that time in between to sort of regroup and rest.
Wife to an awesome stay at home dad and mama to a crazy 2 year old, expecting #2 Jan 3