Just from what i've got

G1 - Soundwave (his tapes make me like him most)
Classics - Jetfire (love the amount of weaponry and clean lines - Henkei OP might take his crown next week though!)
Binaltech - Streak or Skids (haven't opened my Smokescreen! Skids is really underrated IMO - he surprised me cause in box i thought his car mode was ugly compared to all the sports cars in the line - so he was the last Binaltech i bought)
Alternators - Meister (they don't compare to Binaltechs so they deserve their own spot!)
Titanium - WW Starscream (only have one so he wins by default :P)
Movie - Leader Optimus Prime (can thank this guy for getting me back into TF's again)
Masterpiece - Prime or Megs (Prime has the stability and perfect likeness, but Megatron is a more complex and satisfying transformation, and just looks plain awesome)
WST - Soundwave (Recent acquisition, just awesome how he comes with a Ravage smaller than my fingernails!)