I've been a MOTU user since forever, it just keeps on keepin' on, year after year. But if I had to replace it today, assuming I couldn't afford an RME product, I'd probably go with the Roland Octa-Capture. They haven't been around long enough to establish a track record for reliability and longevity, but feature-wise they offer a decent bang:buck ratio.

Hi, Cactus,
     I can run the Studio-Captures at 128 and 256 while tracking in X1 even now. It is only when I use X2 I have had to bump it up to 256 and 512 on the same projects. If I use less CPU hungry plugs, I have gotten down to 64 samples with audio tracks and VSTs running at the same time. The hungry ones, Toontrack, Perfect Space, Kontakt, etc. really chew up cpu pretty good.

Thanks, everybody, for your input!  
 
Sidroe -- your results are encouraging...any plans to try X3?  
 
I haven't built my new system and I haven't ordered the quad capture yet.  There is one on Craigslist that is like new for $150 but I haven't heard back from the seller.  In the meantime, I managed to get X3 installed and running on my Vista 32-bit system but the VST scanner no longer works so I cannot add any new plugins and I cannot use any of the new plugins that came with X3.  It also broke the X2 scanner.  
 
 

I will probably upgrade to X3 in the next week or two. I am in the middle of an album project for a client and I don't like to risk installing an upgrade and everything goes haywire. I'll finish in X2 and then jump. I'm hearing so much positive feedback right now it's making me antsy about getting it.
There was another thread on here about the VST scan breaking and I believe it got solved. It should be fairly close on the list here. I saw it on here several times in the past week.

I looked into the Roland Octa / Studio Capture units awhile ago. (Along with a lot of other units) Nice features for sure. Not so good low latency performance unfortunately.
 
Having said that, I'll repeat what people have been saying for years. RME all the way - if your budget will allow for one.
 
I recently bought an RME UCX. Great unit! Awesome low latency performance. Solid build. Excellent drivers. I could go on and on about all the positives, but it's probably all been said before.
 
 
I was hesitant to spend that much on a new audio interface, but once I started using the UCX and got familiar with the TotalMixFX software (which is great), I have zero regrets and consider it money well spent.

I have to go with interfaces that have more than 8 channels of input. I do a lot of location recording as well. Some church choirs can fill up a 24 and 32 track setup pretty quick. I do have better latency when just recording audio as opposed to a lot of VSTi tracks. I thought 64 samples in ASIO was pretty good. That's about 2.4 msecs.

My needs are very simple: L/R input from my mixer, MIDI in/out, stereo outs.  I have my hardware synths hooked to a mixer and I use a lot of virtual instruments.  The RME looks great, but it's way too much money.
 
@Sidroe -- I found the thread where somebody reported the exact same VST scanning issue I have.  The OP had found a workaround and reported it to CW so I think it might actually get fixed.  If so, then I'll stick with the system I have until X4 comes out and breaks something else.
 

I was referring to "RTL" (round trip latency) which is different kettle of fish. 
RTL figures need to be around or under 5ms or your timing will be off if you monitor using the back end of your system. This is only relevant when using things like real time efx or guitar rig. 
 
RTL is important if you wish to work that way so worth mentioning. 
 
You can test your RTL using this app. 
http://centrance.com/downloads/ltu/
 
 
 

I've had a great experience with the TC Impact Twin. Low latency and outstanding converters. It would have to be pried out of my hands at this point. Great sounding unit.

For what it's worth, the version of the chart that Scott linked to in post #4 is actually from around May of 2013, if not later, so it is fairly current. It was part of my research when trying to decide what to buy to replace my EMU 1820m.
 
Among other things, the chart shows the Focusrite Saffire Pro 24 firewire interface performing very well in relation to its competition, and the accompanying article attributed this to some recent updates to the driver. I eventually purchased the bigger brother, the Saffire Pro 40, and I am very pleased with it. I can confirm the excellent low-latency performance in the dawbench chart, and the mic pres/converters sound very accurate, natural and transparent to my ear.