Gimme those gritty Front Mission style mecha. I want stuff that would completely eat shit on a staircase, ED-209 style! BattleTech has some really neat designs as well. But at the end of the day, I'll take most any kind of mech. Gundams are awesome, Evas are awesome, Orbital Frames are awesome (I could do without the literal cockpit though) and pretty much everything else. I don't care much for super old or goofy designs though. I quite enjoyed Gurren Lagann but the designs of the mecha did not spark joy.
This is really not my thing. Mazinger is probably classic and more influential than god or something, but I wouldn't be able to get over that design. x)