I have all the Jam Packs and consider them all worth having and of equal quality (with the possible exception of the "Voices" pack).

Yes the packs are well produced and full of useful things...

I agree with Beatle128 (voices is my least favorite of the jam packs but they are all worth having). Keep in mind, too, that you can get all the jam packs for 'free' when you purchase Logic. So, if you were heading that direction anyway, it's a good thing to keep in mind. If not, they're cool to get one by one. Also, if you have any connection to a school, you can get the jam packs for about $50 each instead of $100 each. It's worth signing up for a community college class to get the discounts - a place where you can get student/teacher/school administrator discounts online is JourneyEd and, of course, also through Apple Store for Education (their proprietary online store).

Carla whispers words of wisdom.

rhythm is ok. I can't really say much about it since I don't really remember many of the loops that came with it or instrumentation or anything. If you are looking to get any, get symphony.