POB is a lot smaller than JR. It gives it a more intimate feel. It also makes it hard to manuver when it is crowded. POB is less smokey, too--no smoking because they serve food.
Talent-wise, POB is a bit of a mixed bag--seem really talented pianists who can work a crowd, but a couple clunkers as well. (In contrast, I think the guys at JR are uniformly good.) Things get a bit racier than at JR, tho still mostly PG-13. Can be crowded, but can be dead some nights, too.
Last time I checked, I think it was an $8 cover, or $10-$11 for a CityWalk pass.
You didn't ask, but for the sake of completeness, Howl at the Moon is on I-Drive just south of Sand Lake Road, not far from Universal. The biggest of the three dueling piano bars, it still gets packed. Very talented/charismatic players, on a par with JR. Can be a younger crowd than the other two, definitely somewhat of a "meet market." $10 cover on weekends, $5 on weekdays. No food, so smokey like JR. Much racier show than the others; not a place for the prim and proper. Also, usually have drink specials thruout the week, making it a tad more affordable than the others.