Argonians have more panache. A Khajiit would pounce on a rat and kill it. An Argonian would serve it flambee with powdered deer ...

My 2nd and 3rd longest played characters are both Khajiit, so it seems I prefer them, but I have to say I like Argonians, just haven't found the right character-build jet.
That could change though. I just made a new Argonian character, a sneaky assassin called Saelan-Futt. (I just 'Khajiited' the name Silent-Foot) I got plans for this character.
Obviously he will join the DB, but right now I'm training him with some sneaky Dungeon-Diving until some skills are levelled up, mainly Marksman and Illusion.
One of the major plans I have for this character is that he will be living in Flooded Mine after I've completed the related DB quest. I've checked the Construction Set and the crates near the bed in that dungeon are non respawning and I know you can sleep in the bed. (the sacks are respawning)
It's a perfect home for that character from a roleplaying view. I'll just see where all this leads me and maybe the scale will be tipped in favor of Argonians.

Argonians. I other than all the Kahjiit jokes I can think of, the only legitimate thing I might have against them is that their head simply look like a costume mask. I mean their mouths don't fully close when they pronounce their words.

Definitely khajiit. I love cats so its natural for me.

Argonians without question. Why? There is nothing more satisfying then punching a guard and swimming away super fast. Also you can make them look crazy-awesome.