Yes, the Obi is the best so far. Definately brightest, loudest and much more evenly lit than the others.
I would hold off an upgrading your Luke ROTJ for a while... no one knows what MR's plans are, but I for one am hoping the re-release the ROTJ saber; if they are going to do movie-accurate sounds, the ROTJ saber would be the best to do, since it's most distinctive.
Also, the hilt for the current ROTJ is probably the worst - lots of plastic and it just feels like a cheap toy compared to the others (especially the Obi).
Since the ROTJ was never in wide release, I'm hoping MR gives this saber a much-needed upgrade.