It is a protagonist who lacks heroic qualities. While someone like Punisher or Elric can be called antiheroes because of their attitude, Frodo is antihero because of his physical qualities. Hobbits as a whole seem completely designed to exaggerate their lack of heroic qualities. They are small, weak, don't like to adventure, etc.
Personally, I think the fact antihero gets slapped onto someone like Elric more than Frodo is a direct result of how popular antihero stories have been in the last century. I think it is a common view that what makes a hero is less about his physical capacity for the endeavor, and more about the desire,passion,willpower,etc. But I think that was the point in large of the antihero during that time, to show that point. And it did a good job of showing that point, and so people see heroes a little different now days.
If most Conan stores go over 10 pages, it might get up to 20-30. That's still not even a 10th of a normal novel length, let alone LotR. Unless you are starting to count non-Howard books about Conan, going just off word count, LotR has it beat length-wise by double.
"I don't think that Howard has developed themes as well as Tolkien, nor do I think his craft reveals nearly as much skill or love for the language.
But all this is just to say that they're different. They are read for wholly different reasons."
Except for the themes Howard actually wanted to develop. And he might not go to grueling lengths for his 'love of the language', because he decided to focus on things he thought were more important. Like story, character, etc. Why either of them are read is obviously for entertainment. (Well, you might get some freak who wants to read for some kind of academic study
but that would be like one in a thousand at best). Unless you mean something different by the reason you read them.
I agree with what you said about trying to label one as better than the other, but I did give something more specific initially. I said Conan is cooler, as in its more stylish. I find style to be a principle element in how entertaining something is, and have stated that fantasy is primarily for entertainment. And as I posted some time ago in the introduce yourself thread, the strong barbarian is one of my two favorite character archtypes. I site all of this as proof for my original claim that Conan to be better than LotR, subjective as a point as it may be.
Now, one thing I found surprising with the stories is a number of them seem almost like horror stories. Very much like a Lovecraft horror story in fact, the main difference being Conan ends up killing the things that bump in the night instead of suffering a swishy death by them. There are a lot of Cthulhu-type scenes in most of them, but specifically The God In the Bowl, Queen of the Black Coast, Tower of the Elephant (to name a few) would have made good, fairly traditional (minus the time period) Cthulhu stories if Conan had not been there.