The rnc (by fmr) is a nice drum comp, espescially in minimal micing setups if the room sound is nice. the rnc doesn't really impart its own "colour" or "sound" to the signal which really helps it bring out the subtlties of a room. suggested use for the rnc would be perhaps to place it on the bass drum on the way to tape, then over a stereo drum buss during mixdown.
that compresor is without doubt an excellent bang for buck, and will have a permanent place in your studio.
the behringer compressors (autocom, composer) can be good for individual drums like toms, kick or snare, these are dirt cheap, the rnc would do a better job of any of these functions, but you may run out of channels.
finally for drum compressing there is a little one-trick pony that can be had on ebay for next to nothing and that is the dbx 163 (x,b,a etc). it is a very coloured peice of equiptment that is absolute gold on bass drum about 80% of the time, but thats about it. you can use it on bass guitar and some electric guitar too. this is almost more of an "effect" than a tool.
these are units i have had experience with, i hven't had experience with the art pro vla, but i have heard it to be a nice drum buss compressor.
