I loved Amalgam comics, I have every issue of both runs.
Hell, look at my SN...
But if they brought them back I'd want something more conceptually interesting than what's come before. I'd want Marvel and DC's BEST writers on the crossover, and I'd want it to have a central narrative, like one of DC's Crises. Other one-shots would be fine...
Here's what I'd love to see:
Dr. Strangefate - Grant Morrison and J.H. Williams III
Dark Claw Adventures (or even The Legends of Dark Claw) - Paul Dini
Bruce Wayne, Agent of S.H.I.E.L.D. - Greg Rucka
Super-Soldier - Ed Brubaker
X-Patrol - Geoff Johns
Iron Lantern - Warren Ellis
Spider-Boy - Sean McKeever
JLX - Mark Millar
And of course, Generation Hex would be written by Palmiotti and Gray
But it won't happen any time soon... Both companies would rather have major events that they each benefit from separately.