I agree that Kermit will always be Jim's character, however I do think in a lot of ways, Steve has made Kermit his own while still keeping Jim's Kermit alive (if that makes sense).
I can't help but admire the job Steve has not only done for Kermit but for The Muppets in general. I get the sense of a real leadership quality about him that arose either after Jim's death or after Frank left or maybe just in more recent years when the Muppets weren't doing so well and he and Dave became the only original guys left. From reading/listening to interviews with him on the MuppetCast and Tough Pigs, it seems to me that he's fought really hard to bring The Muppets back to the way they were and fought to get David Rudman and Matt Vogel on board to do Richard and Jerry's characters so they can be brought back more permanantly. He seems to take fan opinion seriously and genuinely cares about not just giving his own characters the treatment they deserve, but the other Performer's characters aswell. I'm not saying the other performers don't but I get the sense that Steve has quite a hand (no pun intended) in recent and current Muppet productions.
To go slightly back more on topic, I don't really prefer one Kermit over the other because, despite slight differences with the voice (which took me a while to notice), they're both the same character to me. Although, interestingly - only to me really - whenever I see Kermit merchandise in the stores now (Plush toys, pez dispensers, posters, etc), I always imagine Steve's Kermit talking to me.