PA-12's are wide and pretty comfortable, but tougher to get in and out of with the door post being so far back from the fixed pilot's seat. (and not as easy to hand prop if it still has the stock forward hinged door - compared to a modified clamshell or overhead hinge point with gas strut. I like to prop from behind where I can instantly reach in and control the mixture, mags and power, not in front.)
Nice roll rate and control cables are internal.
I've found that compared to an 18, you have to trim them A LOT. Pretty much every power change.
The one's I've flown also seem a little more squirrely on the ground compared to an 18 or Citabria, but once you're used to it, no biggie.
The fly WAY better light than heavy.
Here's a heavy 160 hp example:


here's a bit lighter 150 hp example:

A bit lighter yet 150 hp airplane

and here is a very light 150 hp example (yes, there is an stc for this mod with the small tail)


and a stock 115 hp PA-12

As mentioned above, need to check the tubing on them if they haven't been replaced before. But good airplane and you'd be happy with one.