At 10 p.m. tonight, inside two of New Orleans best (if most disparate) music venues, two each of the best (if most disparate) up-and-coming local and national bands will do a familiar battle for scant attendance. Its an odd phenomenon: This city in rock terms, at least is sadly prone to long stretches of inactivity and single nights of multiple goings-on. Tonight is a Wednesday. There is no good reason why the two best rock concerts of the week are happening at the same time, on the same night. But indeed they are. At Republic New Orleans, San Diegan (San Diegoan?) rockers Delta Spirit team with the area jazz/pop ensemble Antenna Inn. Six blocks away, Austins Low Lows (above, in a rather amazing video) tackles the Circle Bars cramped quarters with experimental locals Magna Porta. (And thank your lucky stars those bookings werent reversed, or you mightve had one of AIs nine members sipping from your straw.) Call it the Crescent City clubgoers dilemma. The simple math, however fuzzy, breaks down like this: Is a Northern Soul-adopting, mass-harmonizing classic rock redux + a stage-crashing, meter-defying Steely Dan fete > peculiarly voiced, pretty-as-hell indie rock + space-tripping, forever-soloing, Mars Volta-aping prog? My abacus, please.