I've run elite on the cent chassis. Here are my current builds, and an idea for the 9D, which I didn't buy.
9A: very strong hit-and-run zombie. The alpha from 3 SRM6 can rip the rear armor right off an assault, and there's enough spread to make lights very unhappy. I don't recommend XL for the A and AL chasses, because they just aren't fast enough to make up for the fragility. This guy weaves through the brawl, uppercutting the heavies and causing mayhem. Just don't stand and deliver.
Build:
http://mwo.smurfy-ne...880464a16dbe61f
9AL: sneakily damaging build. Hang behind your heavies and peck with your LLasers, isolate and harass.
Build:
http://mwo.smurfy-ne...3be35fd2bd14f38
YLW: I love the arm-mount AC20! The high speed allows for the XL engine (you can grab a Cataphract 3-D or a Muromets if you dislike buying engines without chasses). This guys is a real bob-and-weave boxer, with a ridiculous punch; run circles around their heavies and remove their armor piece by piece. You can drop the extra DHS for more ammo, but I only seldom find myself out of ammo before I either win, die, or lose the arm. Really fun to play though.
Build:
http://mwo.smurfy-ne...98cb4a2711e5b6d
9D: I don't own a 9d, but he sounds like a skirmisher/light hunter built around speed and poking power. As such, I'd make sure to have a big engine, plenty of armor, and weapons designed to take out fast opponents. I stay away from LRMs and SSRMs since the ECM patch; thus the artemis. A little practice makes it easy to hit even fast commandos with them, I've found. The machine guns, while they do basically no damage, are nice for sighting your SRMS. I've done this on other mechs I own.
(theoretical) Build:
http://mwo.smurfy-ne...4a17f57543a1e21
Hope that helps.