I give my vote to Focusrite.  I had a PreSonus but gave it away after using the Focusrite, I thought it was that much better.  The Focusrite software was much more sophisticated, although I wish it had much more flexibility.  (It has (real) multiple mixes, but routing is lacking (and DSP application) compared to say the old EMU 1820 or RME).  Also, I think the pres in the Focusrite are much cleaner.
 
Kind regards,
 
Living Room Rocker
 
 

All the similar units priced in the same range will sound pretty much the same, so it is hard not to go with Roland (a lot of people bought them when Roland owned Cakewalk) and focusrite (which a lot of people here also used).  Since the sound is about the same, finding one that runs on your system w/ no problems is the main thing.  Pick yer poison and make sure it works w/o becoming a tech.  If you have problems, return and switch to the next on your list.  Saving $5-10 for a retailer that won't return is a bad deal.
 
I'm partial to TC Konnect, since I use the 48.  Superb sound, and the sound on the cheaper units is the same.  If the 6 fits your needs, it is a great deal.  However, it is FireWire only (as is the entire line).
 
You might want to go Tascam, since they should be making sure their units work w/ SONAR.  I'm hoping to get their new 7000 stereo unit in for a run, to see if the sound is better than the run of the mill integrated interface.  It is like several other units (RME babyface, the Audient), where the objective is sound quality and fewer channels and higher price to go with it.  They all cost $700 or so.
 
As others have mentioned, the externals matter.  Room, monitoring, mics, preamps can juice your sound cheaper than mere converters - those are all pretty good these days to my ears.  So figure what and how you want to record.  If stereo in suffices, you can go pretty cheap if need be and use the extra money for the above.  If you might want to record a band and need multiple inputs at once, that is different altogether.
 
@

I always have to mention the Akai EIE Pro when I see these threads.
It's not the first thing that comes to mind, but is a very flexible unit. it has no software, other than the drivers. all controls are physical, on the face of the unit.
The original drivers were flaky, but it has been solid using current drivers.
I've had mine for about six months, and I love it.

M-audio, Roland Capture series, Focusrite, RME, Tascam, and maybe a few others are all good choices. You just have to figure out what you want and how much your willing to spend. MOTU is another good choice.

btw, shopping is an art. You don't usually have to pay full fare, but finding the right retailer who can help can be a challenge.

 
A few things you might want to consider...
 
A lot of interfaces, including Roland's, don't have separate controls for monitors and phones, which may force you to reach out to your powered monitors (which may or may not be far away) to turn them off if want to listen just on phones.  I chose a cheap Mackie interface over Roland for this reason.
 
I thought ASIO aggregation was to allow you to have more than one ASIO interface running at once ?  I don't think a great many interfaces support this.
 
If latency is important to you, I'd ask around to determine which interface will give you the least amount.  I believe there is a connection between latency and price.
 
I'd go with RME if I had a choice (which I don't...)
 

My OC has a button that stops the signal from going to the monitors and allowing for headphones only.

Bought the Presonus 16 . 4 . 2 digital mixing desk because, it has 16 ins and outs with faders and many options and effects as well.
I can have a full eight channels for my TD30 kit, the rest for guitars and synths etc.
The channel preamps are not too shabby either.
Although I do tend to use a Focusrite Channel strip for a lot of tracks I still use the presonus for the rest.
Before this I had an old analog Soundcraft mixer and it was a bit unreliable and I was using 2 of the original MOTU 828 units they were rock solid until a spike took them out along with my scsi card and firewire card.
If I had to buy it all again I might buy Either Focusrite or Presonus depending on the features the new units have.
Everything in the computer industry changes so quickly its hard to keep up.
The Presonus for me, has been a great unit, rock solid and dependable.
 
 
 

There are a gazillion choices. Really, the best approach is to make a list of what YOU want from an interface, then look at spec sheets until you find the one that matches up the closest. For example, do you need 5-pin DIN MIDI I/O or not? That draws an instant dividing line if you do.
 
I did a lot of audio tests when I was reviewing interfaces for Harmony Central. They were generally in the same league. I have to say the Avid 3rd Gen MBox interfaces were very impressive in terms of specs, but even an interface like the Mackie Blackjack had extremely low noise and distortion. The biggest quality difference I found among interfaces was crosstalk.
 
As an example of what I mean about choosing an interface that suits your needs, I have separate requirements for the studio or taking something basic for my laptop on trips. For the latter, my prime requirements are small size, ruggedness (able to drop without freaking out), two XLRs with phantom power, 1M high Z input for guitar, SPDIF optical, USB 2.0, and preferably, some built-in DSP for things like reverb in the headphones. I don't need 5-pin DIN MIDI because I carry a little Korg USB keyboard. Quite a few interfaces fit those requirements, but I had a chance to check out the TASCAM US-366 because, well, Gibson owns them so all I had to do was ask .
 
Now, I'm not going to take a piece of gear with me just because it's one of the Gibson brands if it doesn't do the job, or if I can use something better. But as pointed out earlier the differences in interfaces these days tend to relate more to features than specs, and there were two TASCAM features that won me over.
 
First, there's a panel button that calls up the control panel and mixer applet. Admittedly, that's a tiny convenience feature but if I'm doing a seminar or presentation, anything that makes life easier is welcome.
 
Second - and this just goes to show how subjective interfaces are - the small size happens to fit perfectly in my suitcase between two internal "ribs," so there's built in protection against the "Atlanta Airport Luggage Modification Program." Even if the sound quality was only 90% of the other units, fitting in such a way as to provide protection from Delta's elite team of luggage sadists would make my decision for me.

RME UFX!  Best and cleanest DA/AD, GREAT sounding headphone amp and totalmix is amazing with  built-in DSP for monitoring and you can record and capture tracks directly to USB drive.   Unit  and drivers are EXTYREMELY stable.   I had Focusrite Saffire 56 and that worked great.   One big diffefrence (for me) is that the RME line ins DO  NOT go through any  preamp circuit but focusrite does so if you hook up external preamps you are guaranteed to not get any additional coloration.   Its pricey but I should have spent the money in the first place! This is documented and true.   The differences are small  but they are noticeable.