It really depends on "exactly" what you want out of the game. I have both the pro and the premium. I too swore I would not get a pro, but got one to do my light mod development on, and I actually like it a lot.

Premium..
The swinging bell is a SWEET shot. I love it.
Lower playfield, I hardly EVER use it.
Drop targets, I LOVE drop targets and this is big for me.
Colour changing inserts, very cool but not a deal breaker,
Colour GI, again very cool, but that's why I built the light mod, so I have the mode-locking colour GI.

Pro..
Angus face, fugly, but I have a sweet Helen decal over it.
FAST, and I mean brutal. The pro has no momentum taken out of the ball by any drops so absolutely FLIES around the playfield.

To choose between the two you have to be clear in your head exactly which of the differences are important to you. I can say though, that during gameplay I totally forget which one I'm on except I get my arse handed to me more by the pro.