I think Tekkit is a bit outdated, and slightly illicit in terms of asking the mod creators for permission when using them in the package.
I found FTB to be both similar and better than Tekkit in many ways such as compability, updates etc. I had the outmost terrible luck playing on a server where one in the admin team was corrupted, and nobody did something about it. I later moved on to a community where I had been before, and I was known and recognized. It was a shame this server shut down though, for whatever reasons (sure as hell wasn't budget, I can tell you that).
Used to run a gameserver with a couple of friends. JH Gaming was the name.
Was a full 70 slot server back in it's hay day, nothing especially massive but we weren't rich enough to afford any more. Then we ran into a lot of problems with our Host being incapable of building servers properly. Dislodged CPU fan kept the server down for days. Killed it completely. Was a shame, was a lot of fun to admin and build.
We're looking into reviving it under a new name and new version of Tekkit (Modern instead of the previous Classic) but it's a lot of work. We are however pretty bored and want to make it work again.
FTB was just too much. It was getting too ridiculous. The anti-lag features worked extremely well and we ran FTB for a while. I didn't like it so much though, prefer Tekkit by a long way. My fellow head admins shared the same notion.