Roland Octacapture or Focusrite 18i20 ????

All I can suggest is that you read reviews about both of them, or go by reviews from users taking those with a grain of salt so to say.
 

I have an Octa-Capture.  It works great and I wouldn't consider (now at least) anything else.  I had a Focusrite Saffire Pro 40 that I loved, but it died out of the 1 year warranty (and the repair cost from the authorized Focusrite US repair center - Focusrite US does not repair anything - was within $40 of what I paid for it) that I dumped.
 
The Octa-Capture has built in limiters and compressors.  I use the limiters quite a bit when I'm recording and also playing steel at the same time as I can set up the vocal or other instruments and not have to worry about levels.
 
Given the Focusrite repair situation, if it ever needed fixed in or out of warranty, I would not consider another Focusrite product.  On the other hand, I don't know what Roland's repair (in or out of warranty) is so maybe the bad situation with Focusrite isn't really an issue?
 
Generally acknowledge music audio guru Craig Anderton gave the Octa-Capture a glowing review.  

When I contacted Focusrite, in England, I was referred to the US distributor.  The distributer referred me to the company in N. Las Vegas that is the third party factory repair for Focusrite.  Their price quote to me included their 2 hour minimum labor charge @$100 per hour ($200) plus the cost of a new main board in the Saffire Pro 40 which was $200.  That was $400 (plus shipping both ways).  I only paid $440 for the unit, new.
 
 

The biggest thing w/ the low to mid end of the interface market is drivers - and how they interact w/ your specific computer.  So read the reviews and specs and pick whichever one best suits your needs and fancy.  Hardware wise, there won't be that much difference.  Certianly not enough to warrent spending a week trying to get X interface to work w/ your computer while y works like a charm from the gitgo.  Just be sure that you can return the unit and exchange - support your local music dealer even if it is only guitar center.  Much better to take it back rather than wait a week for a return/reship.  Of course, there is the long term concern of support like Fireberd says.
 
Unless you have a reason, I'd try the roland.  Sonar and Roland ought to work right out of the box, but there are plenty of others here that use the focusrite family.
 
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Thanks to everyone who has weighed in on this!  After much thought and a good talk with a Sweetwater sales rep I decided to go with the Focusrite 18i20.  I really think I couldn't go wrong with either product - I will let you all know how it turns out in a week or so.

Still really liking the 18i20, the addition of the 8 I/O's has made the recording process much more flexible to my needs.  The Scarlett MixControl is starting to make some sense....
 
The only glitch so far - the preamps in the 18i20 don't seem to have adequate gain for my Cascade Fathead II ribbon microphone.  I have an email into Focusrite asking about this- but haven't heard back yet.  In the meantime, I have opted to run the Fathead into my Aphex mic pre and then into the 18i20 at line level - which works great.  My other condenser and dynamic microphones work fine directly into the 18i20.

To back up a little, trusting a review by a persons review who is possibly biased due to monetary gains from a company ? Careful with those glowing reviews from the "industry". One has to be care full with all reviews. In a way I trust user reviews more than the ones from the so called Pros.  
User reviews need a lot of filtering but you can normally get a "feel" for a products good/bad list.
My favorite is a review by someone who just bought something yesterday and is all fired up about it... Lets see a follow up after you live with something for a while. Those are the reviews I will more or less trust. It will start with, "I have owned this for a year or so now". 
You can also tell sometimes if the reviewer is just a regular bloke. I never trust any review that states " this is a complete piece of rubbish"  This person most likely either got a defective unit or is incompetent at using gear.