I find the DW20 and Unleashed pack to be equally as fun. The Unleashed pack has the most mods so there is potentially more to play with but this doesn't mean it is more fun than the others. My server runs the Unleashed pack ATM and I find myself missing gregtech at times. I went with the Unleashed pack because of soulshards and portal guns mostly but found that I don't really use either very much.
Long story short, it is really all about what you want from the game. If you want slower game progression go with Unhindged if you want to focus on building and creating different systems Dw20 or Unleashed might be a better choice (but you can still do this with Unhindged). I find it hard to decided which pack I like the most...
