I always here people in MLG complaining about Lockdown but truthfully, I don't really mind it. It's pretty straightforward, the spawns aren't rediculous (see below), it has some decent cover, and there's several ways to set up.
But don't even get me started on Amplified...

If any map needs to be taken out, it's Amplified, just because of the degree of rediculousness (is that a word?) of the spawns.
I think Assembly would make a great MLG map though. It'd be perfect for Slayer or CTF (oddball or King would get too restricted in the sense that there's limited angles of attack). I also hope that someone will make a decent large sized map out of Sandbox too. There's definitley enough of those mid-sized symmetrical maps, we need a change.