This is a pretty obvious answer to me, and it seems to be the same as most everyone here, which is that the JLA would wipe out the X-Men with little to no effort. Like a few have said, it is also because the power scale is substantially different. I haven't looked around too much yet but if there's a poll here on JLA vs. the Avengers ...

I put down X-Men, because I'm all for the underdog.
Besides, Professor X would anticipate the attack, so they would hide somewhere save (I'll leave it at someone else to determine were that place could be).

Finally, they'd throw out Wolverine, so the Justice League has something to play with until they all die of boredom because he regenerates (for the sake of the argument I assume that they won't find a way to stop that - but given the enormous number of Wolverine-titles Marvel is running, I doubt they will).

I think the X-Men could give them a run for their money since they can fight dirtier and are more sneaky. However, if they should defeat all of the JLA, they still have to account for Batman and he always has a trick or two up his sleeve.

this is kind of tough. i mean you could say that the JLA would slaughter the xmen but who's to say that professor x is at his normal level and no onslaught? whos to say that the phoenix/jean grey doesnt come out of her little area somewhere in the galaxy and join the xmen. and whos to say that its just the original xmen. i mean there are some pretty powerful mutants out there. ones that neutralize powers, ones that stuff happens based on what they think. the xmen in my opinion are underrated in this fight. i think heroes like superman and flash would be beaten before people think they would.

x men should win and as for superman just have wolverine dip his claws in kriptonite

All powers aside, JLA (at least in the past decade) is just written better. So my vote goes to them.

And for the record, I'm not denying that there have been some great X stories . . . just overall, I feel that JLA and Co. have been more interesting.

Hands down Justice League to trash the X-Men...
Nah Rogue can't absorb all their powers...she'll go nuts...anyway the only edge X-Men have over JL is psychic attacks but hell JL would still win w e sheer numbers