[David603]

Ultrapack 2.0 uses HSFX 4.1 as a basis so content is pretty similar between the packs, though 2.0 has a few extra planes. 2.0 also has the latest version of Zuti's Moving Dogfight Server, where 4.1 has an older version. Since 2.0 has a switcher to allow you to use your 2.0 install as a 4.1 install, I would go for 2.0 and use the switcher if you want to play in a server running 4.1.

Hope that helps.

Regards

EDIT: This was posted before I saw the other two replies, so don't feel I'm just repeating what they said