Currently I use a Duo-RX as my main system and a PCE/Coregrafx+Booster Super CD Rom as backup.
Oddly I've never had any accuracy issues with the RX's pad/Arcade Pad 6. I just tested again to make sure I wasn't wrong about it, with Street Fighter II' and I was able to pull off every high level combo with no mistakes or unwanted inputs, its perfectly accurate. I did find some things I felt made it not perfect; the unneccesary thickness of the pad on the outer bottom, and the raised middle portion would cause my finger to hit it instead of the "IV" button until I adjusted for it. Also, the edges of the d-pad are sharp and can cause discomfort if you like to "slide" your thumb on it to get your moves off. But it is by no means inaccurate. I have 2 of these pads (both in mint condition), as I wanted one for each of my setups, and even though I got a really good deal on one, they are really overpriced.
I have a ton Avenue Pad 6's and they're okay, I'd rate the Hori Fighting Commander PC a notch higher but I found it will sometimes cause the system to crash if you plug it in with the power turned on. Since I got the RX pads I haven't gone back, and to be honest I didn't know people didn't like them till I read this thread, since they sell for such a high price. I was considering doing a mod for it so I could use the III button as the run/select as if it were an Avenue Pad 3, but the stupid thing is worth too much so I'm having second thoughts.. oh well.