My guess would be one of the three founders, both because they've been around longer and because of the number of stories referencing the first Legion story in some way. But I don't know for sure.

If honorary members count, then Jimmy Olsen in a landslide.

Otherwise...Probably one of the founders, and my vague belief is that Saturn Girl would be the one of those who's been off the team the least often. Then the other two, probably with Lightning Lad in from of Cosmic Boy.

After the founders, I'd say the next spot would be a race between Braniac 5 and Phantom Girl, with Mon-El, Karate Kid, and Triplicate Girl a bit behind them. [All of these listed in descending order.] But these are all just guesses on my part

Jeff, I had in mind full-fledged members, so Jimmy and Lana don't count. Obviously, you're right that Jimmy would win in a landslide if he counts.

My thought was Ultra Boy. It seems like he's spent more time as a popular Legionnaire than anyone else, which means I would expect him to have showed up in more stories.

Ultra Boy is fairly popular, but he's been off the team in large stretches and was introduced relatively late.

The last three I mentioned (Lar, Val, and Lournu) have an edge in that they all have appeared outside the Legion books quite frequently...in fact, that may vault one of them over the founders.

The appearances lists on dc.wikia.com has (for the pre-Zero Hour versions) Garth at 133 appearances, Rokk at 151, Lar at 126, Jo at 105, and Val at 72.

It also has Imra at 141, Vi at 90, Luornu at 77, and Tinya at 76.

These numbers will change if the post-Zero Hour and New Earth versions are added in, but given how central Rokk and Imra are to both of those versions throughout their lifespans, i think it's safe to make them the winners (unless you want to multiply Luornu's appearances).

I think those DC wikia lists are incomplete. They've got Ultra Boy appearing a mere 7 times during the Superboy & the LSH/V2 era, and that can't possibly be right. I demand a recount!

You're correct, of course. Many of the entries for the Superboy era just have the covers. However, I'm not sure that even counting those will get Jo above Rokk (who appeared in a number of the issues not counted as well).

This is a question for Michael Grabois...

I'm going to guess, and I freely admit I could be wrong, but I going to guess Tellus.

(Lar Gand made a bunch of appearances in various places when they were trying to pump up Valor in the early 1990's.)

According to Arthur Lewandowski (of the Legion APAs Klordny and Interlac), who has been tabulated an amazing Legion appearance chart through to the end of 2008, the top five Legionnaires are
Brainiac 5 (9910 appearances)
Saturn Girl (9547 appearances)
Cosmic Boy (9468 appearances)
Lightning Lad (7183 appearances)
and Mon-el (6752 appearances)

I got nothin'.

I do, however, have the appearance list from just the Adventure Comics issues, for what that's worth, from the Comic Treadmill:

The first number is how many "quiet" appearances they had, typically in background not doing anything. The second is how many "active" appearances. Sorry for the formatting.

Superboy/Superman.....2.....85
Saturn Girl.....5.....72
Brainiac 5.....8.....61
Cosmic Boy.....11.....59
Sun Boy.....14.....52
Lightning Lad.....12.....51
Chameleon Boy.....14.....46
Ultra Boy.....6.....43
Mon-El.....11.....40
Duo Damsel.....13.....37

Thanks for posting those numbers, Murray. I must admit they seem a little high to me (it gives the top three each roughly 200 appearances per year since they first appeared). Unless we're talking panels or pages, as opposed to issues.

Even pnaels seems a bit on the high side... In fact, I call shenanigans. I don't believe those figures.

I've found more complete listings on comicvine.com, which gives numbers by issues. The problem is this also covers appearances in reprints, archives, who's who, etc.

The results for the Legion men:

Brainiac Five: 550 issues
Ultra Boy: 405
Cosmic Boy: 507
Lightning Lad: 484
Karate Kid: 248
Mon-El: 408
Sun Boy: 352
Star Boy: 287

The ladies:

Saturn Girl: 565
Phantom Girl: 375
Triplicate Girl: 325
Shadow Lass: 309
Shrinking Violet: 339

And for Mike:

Tellus: 57

For Jason: Arthur was counting appearances in panels. At the beginning of his appearance chart he goes into quite a bit of detail about the hows and whys (he didn't count cover appearances, he did count splash pages and roll calls, how he would deal with impostors (like Yera), which issues would be included/excluded, etc.). It's all quite detailed, but far too long to post here. He breaks appearances down into totals by year, by era, by issue, by character. It's a cool piece of work and certainly something to track down if you're at all interested.

For Mike: Shenanigans on you! Have you got different figures? Have you done some counting on your own? By all means, then, please post your own figures.

Mike tells me he's replied to this thread, but his reply obviously hasn't been cleared...

I don't know that I need to justify not believing something. The reason I don't believe it is that it's claiming Brainiac 5 has made almost 3000 more appearances than Lightning Lad. If it's panels, I find it to be a useless metric, but I suppose it's posible that B5 could have appeaed in 100 more comics than Lightning Lad.

I'd find it easy to believe that Brainy's appeared in a lot more panels than Garth. In a lot of stories, Garth's a background or cannon fodder/crowd scene type character. Brainy, when he's in a story, tends to be a significant part of it, probably because "super-intelligence" is a lot better for moving a plot along than "super-lightning".

Michael Grabois's comment somehow found its way into our spam filter, so it didn't get posted until now. Apologies to Mike -- everyone else, go back and read comment #11 (but ignore the part where he says Ultra Boy had fewer apeparances than several other characters, since that's obviously a pernicious lie spread by those who are trying to belittle Ultra Boy's popularity).