Well, let me start off dating myself. I watched the first run when it came out. It was in B&W when it started. Robert Conrad (James West) was the James T Kirk of westerns is how I would put it. Robert Conrad was 200% better playing James West than Will Smith. And while Kevin Kline did a decent job as Arte. Ross Martin was a better Arte.
200% better? That's an INSULT! He was freaking OFF THE CHARTS! The BEST however, was Michael Dunn as Miguelito Loveless. He stole any episode he was on...He was simply a brilliant actor in that role.