At certain point I've found conversion to be far less important then a lot of engineers seem to dress it up to being. I've used M-audio, alesis low end and high end convertors, m-audio, PreSonus, motu, echo, RME, apogee, API and more. The line that conversion doesn't matter to me is at the RME line. M-audio, presonus, alesis masterlink, echo, motu are all under that line. Alesis adat hd's are fine, RME, Apogee and the like are fantastic. I'm not saying that the analog part of a BURL isn't all this and then some but my previous statement is were I draw the line. In the lower end I like presonus stuff and I could be fine with motu. The cheaper the conversion the better you need to be at tracking and the better front end you'll need to have. So overall the cheapest is RME and a good clean pre. I tend to not like clean pre's as much with presonus and motu convertors so I end up using API or something else. On the other hand an Audient 8 channel pre into an RME will get you a pretty solid chain. That will be 3k for 8 channel of pre's and conversion which is pretty unbeatable.
I am quite happy using my ensemble and RME convertors.