Welcome to the forum!

As you undoubtedly already know, both the ProPAK and MegaPAK include the full version of Band-in-a-Box for Mac. However, both packages have limited content compared against the amount of content available in the UltraPAK or Audiophile PAK.

My advice is to get the largest package you can afford with the intent of learning as many program features as you can. Many new users concentrate on the content and become frustrated at not being able to use styles, RealTracks or RealDrums that are not available to them. You can avoid much of that frustration by enjoying what you have and learning the program.

The MegaPAK has about three times the content as the ProPAK so you will get frustrated less often if you have the MegaPAK. However if you want to learn to become proficient and efficient using the program and it's features the ProPAK works just as good as the MegaPAK.

I started with the ProPAK. While learning the program and features I saved my money with the understanding I could upgrade to the UltraPAK during a new release sale.
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Jim Fogle - 2021 BiaB (829) RB (Build 5) Ultra+ PAK
Cakewalk - Zoom MRS-8 recorder
Desktop: i7 Win 10 build 2004, 12GB ram 256GB SSD, 4 TB HDD
Laptop: i3 64bit Win 10 build 2004, 8GB ram 500GB HDD
Music at: http://fogle622.wix.com/fogle622-audio-home