I wouldn't believe anyone that hasn't tried both. Most reviews are from those that like what the bought.
That said, I recently (with the last two weeks) tested 4 shocks on one bike.
I have a new carbon nomad. I also am a signals analysis engineer, working nor proper dampening... From an electrical point of view, but the principles are the same.
I tested a Dhx 5.0 air, RC4, rp23, and a vivid air. I ran different settings on each to get it as dialed in as possible. Sag was the same on all. I am not a RS fan typically, hence all the fox shocks I own.
I'll spare the reviews for those that you don't mention, unless you'd like me to elaborate.
rp23: brand new 2012 Kashima coated shock. Nice shock! For the nomad platform, it did better than the Dhx. Most small bump absorption was still a little harsh, despite modifying the rebound and compression,mi couldn't get this smoother no matter what. I removed the air a little, and got better small bump absorption, but at the cost of blowing through travel faster. Bigger hits were nice, but again you need to increase the compression dampening to get that endless feel; but at the cost of no small bump compliance.
Dhx 5.0 air. A 2010 model, recently serviced. I struggled with this shock on my original nomad. With the piggy back air chamber, this helped the small bump compliance balance out with the big hit category ( see above). However, when I stepped on the gas, the larger air chamber gave me some odd kickback on the bike. I could minimize this with by making the top air chamber a little smaller in volume ( bottom out setting makes it more or less progressive). This was my first really good shock I had on my original nomad... But I hadn't ridden anything else.
Vivid air: I had the ability to test one of these shocks out last fall on my original nomad. I was a complete skeptic. RS doesn't make good shocks, right? Fox is the defecto standard. I opened up and tried it out, trying to keep an open mind.
This shock is simply amazing. When it first started my ride, I swear I thought my tires were going flat. I checked the, twice. What it was, was the incredibly smooth small bump absorption. Once is figured that out, I thought it might not be in the right sag setting. Hmmm, duped again. The sag was still as we had set it up. This was completely new compared to both the rp23 and the Dhx air. I started with some technical up hills. Usually my fox shocks lose their travel, and lose traction over the small bumps when the shock was compressed into half it's travel (cg is mostly on the rear tire). The vivid air simply did as advertised.... It smoothed out the ups even when the terrain was rocky. I had many firsts and dab less technical uphills compared to my fox. This is too good to be true, right?
On the flats, I stomped on the pedals. I got very little feedback. Nomads are famous for this, and the shock did give me some of that, but not as much. The fox's can overcome that by switching the stable platform settings, but at the cost of traction in the rock piles.
When I turned the thing downhill, this was where the shock is really supposed to perform. Nothing could beat my RC4... So I thought. The air was a little too high, Suomi took out 10 psi. The rebound was packing up, so I clicked that back by a click or two from the initial settings. All was good. The shock tracked better than any coil I had tried! Unbelievable. The new settings held their ground when doing the last few climbs. Simply put, this shock did it all. I was expecting a worse performance out of this shock tha the Dhx air. But I was completely wrong.
In the end, I simply couldn't believe it. The RS surpassed my expectations. I feel horrible, beause I had just bought an RC 4 a few months prior. I had signed up for the rock shox experience to test new forks, but the RS guys insisted I try the vivid air.
I ran all four shocks on my 2012 nomad just for fun. The best to worst performing shocks in my opinion are below.
1. Vivid air
2. RC 4 (the coil is awesome, but it's heavy'. I need a spring between the two they offer)
4. DHX 5.0 air
I just sold my new rp23 and Dhx. I'm now thoroughly convinced that fox is a marketing machine and does well with marginally performing shocks.
I just recently (yesterday) took delivery on another vivid Air to replace my RC 4 on my Santa Cruz v10. I'll keep my RC 4's around for certain conditions. But this shock is the best one I've tested yet.
I've heard great things about the monarch, and still want to test out the cane creek double barrel