What are the major differences between these packs and which one should I rather play ?
I don't means to cause any wars !!
If by beta, you mean the beta pack A, then that's a legacy pack, that's no longer updated. It's not compatible with other worlds, and will be removed shortly.
If you mean the 1.5.2 beta, then the main difference is that Ultimate is still 1.4.7, but fully supported. There are some mods added/removed, but that's mainly down to what's available for the version, and there are things added/removed/rebalanced in each mod within the packs.
The Beta is beta only, and not guaranteed support or future-proofing. The teams have said that future packs and IDs will not be compatible.