You certainly get to know your instructor particularly well in the 152
...and thereby lies the rub (literally!)
The human race is getting bigger, particularly in the West. I've several hundred hours in PA28s and they certainly afford more room and have better load-carrying capabilities.
Now, as to which is BETTER for learning on...
I did my FI course on the 152 and I do believe that it is the better aircraft in which to teach and learn the basics of the effects of controls etc. It is more 'honest' in terms of the reaction to control inputs. For instance, you can get the aircraft to show adverse yaw upon application of aileron, something I've had great difficulty in showing on the PA28. The stall characteristics are also more akin to the 'classic' indications/symptoms. The main undercarriage on the 152 is pretty robust, though both can soak up an amazing amount of punishment. The main difference is that the oleos on the PA28 will absorb vertical motion better; if you 'drop' a 152 the sprung u/c will throw you back up into the air again, leaving you without airspeed or ideas.
I had a student recently who flowed over the P1 seat in a PA28 to the extent he had a problem getting at the trim. I'm not small either (6'2") so we wouldn't have had a chance of even fitting in a C152.
We had a 152 recently available for a couple of days so an instructor colleague and I grabbed the keys to go and do some spinning; don't get too much chance these days. Unfortuantely with the fuel on board and our bulk, although we were JUST inside the W & B envelope, the CofG was just too far forward for it to spin or indeed stall properly. Of course the Warrior isn't approved for spinning, so we can't try it out. We do teach stalling in the Warrior, I do agree it's very benign but you can go through the recovery drill which hopefully will stand the pilot in good stead if the worst should happen in another type. A checkout in a different type should include stall and incipient spin recovery, anyway.
PA28 better on grass? Depends upon the relative smoothness of the grass, I suppose! (sorry David)
Cheer,
TheOddOne