I've been in this exact same position recently. I've used an HD500 with my triple rec for about 4 years now, and while it sounds great, it does have some tone suck, and I wanted to be able to better integrate a few pedals into my rig. Adam and James helped me narrow it down to a few choices already mentioned in this thread:
TC G System
Axe FX (older model, ultra or standard, just for effects)
Non 4CM effects processors:
TC G Major 2, TC Nova System
I'm not going to say which one I went with because that's still in-process, but those seem to be the consensus models with the least amount of tone-suck and the most robust effects in 4CM. For the price you can't beat the GSP1101, though you will need to get a floor-controller for it. The upgraded mustbebeta firmware for it is a must, as it comes with updated effects and the ability to load IRs. The G Major 2 is a rack staple and sounds great, but the menu can be difficult to program.
To be perfectly fair, the G-System price point has come way down since Fractal, Kemper, and Line 6 began offerring serious products in that $1500-$2000 price range. A new G system is $900 (on Sweetwater.com), used they go for $400-750 and sometimes come bundled with a MIDI switchable drive pedal called the Nova Drive.
I can personally vouch for TC and Fractal effects, I do not believe I've heard better for guitar than those companies make. I've owned a G-Force and an AFX Ultra in the past, and both were absolute behemoths. I would shy you away from the G-Force though, as it's a dated unit with tone suck and it cannot do 4CM.