I'm really tempted to get a centurion or a dragon mech, as I do not currently own a medium mech and I love being mobile! I know a dragon is actually a heavy mech but I feel it should be played like a medium!
Never tried a Centurion but Dragons are one of my favs. My usual rides are Fang and Flame but these are good. The first is actually an identical build to what I run on the Fang:
one of the champion/trial mechs a while back was a Dragon with Gauss & 2 Large Lasers. All of the Dragons can run that build with an XL300 engine and it's a good loadout.
I would never run anything less than a 300 engine in a Dragon, personally. That gives you 81/89 kph speed.