I was ready to purchase the Roland Octacapture.... but now see that the Focusrite 18i20 may be just as good for my purposes.
I use an older Dell Desktop with an Intel duo core and 8 gigs of RAM with Sonar X2. I also use  Ozone, Alloy and a lot of Toontrack plugins.
I am most interested in reliability -  ( the electronics, the drivers and compatibility with Sonar).   I am also interested in ease of use and flexibility in setting up various monitor mixes.  They both seem to fit my needs nicely - so probably splitting hairs - but any knowledgeable input/experience with either of these would be greatly appreciated!
 

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.
 

Yeah - that's what I have been doing. Just wanted to see if any Sonar users have anything to add
about either one of these products.  Every once in a while a product will look real good in the advertisements but not live up to the hype - or have specific issues with certain setups. 

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.  

Thanks Fireberd - for sharing your experience with Focusrite support.  That is exactly the type of situation that I wish to avoid.  I did read Craig Anderton's review of the Octa-Capture - one of the reasons I am so interested in it.

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.
 
 

I bought a new Focusrite Scarlett 18i20 a month ago to replace a Presonus Firestudio Project and I' am very happy with it.
Preamps are great, I'd say a little more warm and full than the XMAX on the FSP.
I always record audio monitoring thru software fx and there is no problem doing that with the 18i20.
 
Of course I can't comment on reliability cause my interface is new but, the mix control application is IMO very easy to use, and you can route inputs and outputs almost every imaginable combination.
 
In my case, I just installed the drivers and software and the scarlett connected immediately to my laptop with no glitches. I love that I can turn it on and off at any moment and it just syncs with the computer every time.
 
I have no experience with the Octacapture but I love the Focusrite Scarlett 18i20!!
 
Hope this helps.

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.
 
@

There is a long thread on the gearslutz site about the Focusrite 18i20.  Good and bad.  http://www.gearslutz.com/...te-scarlett-18i20.html

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.