Well? Fiberglass or Urethane? which is better for a body kit, what are the differences? I want the Sinsei evo front bumper, blitz side skrts and bltz rear

Sensei front is only in fiberglass. I say fiberglass because it's easily modifiable, but others will disagree. It's a long going debate. Probably 90% of kits are fiberglass, and two years ago, almost all kits were fiberglass (blitz wasn't even available in urethane).