as others have mentioned previously, this is hard. overall, i think loop ash, ps and undercode are pretty much equal as they satisfy different music tastes. midi:nette needs to produce more bands before they can really be considered a label, i think.
PS and undercode are pretty much the same - lots of bands, lots of evil marketing plans, but all-in-all, while not excellent, they are decent. i really like due' le quartz's 1st two releases, and kagrra is not bad either. undercode somewhat satisfies my desire for heavier visual kei, but not quite right yet. but i do like dari/dali, siva [why did blast have to disband?] and nega.
loop ash, michiru is sweet, but he and misa worked better together in my opinion.
and what about applause records? kamijo [lareine]'s recording company. lareine rocks, and isabel varosa is pretty good, and belles had promise (but maya retired from the scene). but then, i guess it is a bit like midi:nette in that not very many bands.
but my fave label of all time has to be key party/enamel. soilel and kappa records are also not bad. and i have a soft spot of exctasy records - x, hypermania, zi:kill!