I wouldn't like to see any of those 2 go..
I'm for trying to stop Twilight and Mystcraft integration.. I'm still kinda new to all ftb and I would hate to see any of the mods go since I'm really enjoying myself getting to know those mods.. (I'm yet to slay an Ur-Ghast..
)
Twilight is cool cause it gives exploring in minecraft more meaning (also more mob diversity and if we get gravi gun back, best way of getting nether stars) and Mystraft is awesome for many things (such as doing bee research in an all day, no weather age really helps, also what Draze said, ppl would just use QuarryPlus to mine out all Overworld)..
Another note, I would really like if we could get the new updated DartCraft, since it' more balanced and introduces many very useful and fun items..
(if we don't get gravy gun, it would be good to at least get force wrench back..)