I don't want to make this a JMS vs. RDM vs. JW thread, unless that's the will of the board, so I'll respond and then hold my peace.
Whedon's strenghts are JMS' weaknesses .. and vice versa, as I see it.
Whedon writes great dialogue, where JMS can verge into cheesiness way too easily at times. Whedon is a team player, and can organize a writing staff spectacularly, while JMS .. wrote X-thousand episodes of B5 on his own for a reason.
At the same time, JMS manages grand epic arcs of the sort Whedon doesn't even try to touch. Whedon's work don't have the socio-political depth JMS' works have. While I we can spend hours and hours debating if the Minbari suck or not, even 10 years after B5 went after the air .. we won't be debating weather Glory sucked or not 10 years after Buffy went off the air. And, in spite of being good shows in the end, Joss shows are based on completely silly ideas. (Buffy the Vampire Slayer? Western in Space? Just think about it .. ignoring that you know that the shows don't suck.)
If the two ever have a lovechild, it will be too much awesome to take. But I personally don't see the point of claiming that one is "better" than the other. As & Os.
Whedon may not have done the grand plot arc, but the character arcs are there in spades. There's a reason I can claim (and get some real scholarly backup for it) that Spike is the best character in fiction -- his character arc is insanely good. And over on the Whedon fansite I frequent we're definitely still discussing the show ten years later (since the first airing). Heck, every time I watch the musical episode I catch something new... something
new, something I've never noticed or realized before, after 15 viewings and five or six years!
And while I need JMS's words, I resolved some time ago that I'd teach part of the Buffy episode "Earshot" to every class I ever run, because it's something that every teenager needs to hear. There are people alive today because they saw something Whedon wrote when they were hitting bottom.
I will grant you that Whedon's chief weakness is that his shows can't be summarized.
From the little Buffy I've seen, and all of Firefly/Serenity, Whedon's famed dialogue and characters are very "hip" and clever and while it can be entertaining, the weight and themes involved in B5 just make any comparison moot, IMO, for some of the reasons Chilli went into. But what it all means to me is that B5, at its best, is so much more adult than the rest.
You haven't seen The Body, then... I'll grant you that Whedon's shows seem escapist and juvenile at first, but Buffy/Angel grew increasingly dark and mature as the show went on. Firefly probably would have topped them both if it had been allowed to live.
One last thing: some years ago a couple discovered Buffy. The wife of this couple, Robin, is schizophrenic; she latched onto the show and used it to try and keep herself stable. When the husband wrote about this for a contest, Joss found out about it, contacted them, learned more, and then
wrote Robin into the Buffy universe in such a way that contributed to the plot and also deftly made a metaphor of her condition. It was beautiful. When Robin herself read the story, she was going through a bad spell. Her husband simply pointed out that if everything in her head was real, then Buffy was real too. Robin paused to consider this, said, "You're right. Buffy's got my back," and calmed down.
So: Joss Whedon's words can prevail over schizophrenia. Or at least they did once. Top that, Ron Moore!