In terms of "all time", I'd have to say...

1) Heavyweight
2) Welterweight
3) Middleweight

I know that the guys in lower divisions are much more skilled than the bulky HWs, but to me the biggest attraction is always the HW division, because (at least on paper) the #1 HW is the guy who can whip ANY MAN in the ring. The HW champ SHOULD be the baddest man on the planet.

Right now, my favorite is the Welterweight to Light middleweight area. Just so much talent and such a diverse talent pool. You have established living legends like Pacquaio and Mayweather, you have budding stars like Canelo, solid wild card guys like Berto, Guerrero, ect, and exciting prospects like Keith Thurman. I really enjoy that range of weight right now.