Here's all the noise gates I've played around with... I prefer noise gates as opposed to suppressors (I think that its best to keep the amp's tone unaltered and just kill the the feedback / white noise when you're not playing).
I use an NS-2 with my 5150, with the 4 cable method (input (pedal) - Guitar, output (pedal) - effects return, return (pedal) - effects send, send (pedal) - amp input; I think that's what it is, but I'm not 100% sure, it shows you this setup in the manual for the pedal) and it makes my amp completely silent, to the point of not hearing anything coming out of the speaker until you play and doesn't alter the tone at all. The key is to use in 'gate' mode not noise reduction mode, the reduction mode just doesn't seem to work right. If you just throw it in the loop alone you're still gonna get feedback here and there, probably, and if you throw it just in front you'll get a lot of white noise. As far as value oriented noise gates, this is the way to go. ~$70 brand new...
I have an NF-1 that I let the other guitar player in my band use. Works pretty well, doesn't really effect tone too much, but doesn't get all the feedback especially during quick stops. Bottom line: Pretty good but the NS-2 is better.
ISP Decimator pedal version is excellent, very NF-1 like, but completely transparent. Probably the best pedal noise gate out there, but value wise I'd take the NS-2 over it.
ISP Decimator rackmount is amazing. Completely transparent (like my above implimentation of the NS-2). No matter the gain setting it does probably the best job out of any noise gate I've played with. Takes a while to tweak properly, but once you get it setup then you won't hear feedback. The best rackmount noise gate that I've used.
Rocktron Hush / IICX rackmounts both were terrible and tone suckers.
Rocktron Hush "The Pedal" (single channel) absolutely sucked. Sucked tone immensely and created a ton of extra white noise (which led to a lot of just hissing).
Rocktron Hush "The Pedal" (dual channel) was okay. Sucked a fair amount of tone but didn't create so much white noise. I wonder if the Arch Enemy guys had theirs modded?