I own Behringer's Ultra and Ultra-G along with 2 Whirlwind IMPs. I've used the listed Radial AV1 and the Countryman DI. Radial's stuff seems to be nearly bullet proof - built to last, transparent in the application I use it for which is live sound for AV presentations. The Behringers were a gamble, but I like them better than the IMPs - a more robust signal through the Behringers with a variety of guitars; again in a live sound situation. The Countrymans are solid also - only used these in a studio situation and did not have any other DIs to compare to at the time. Pricier than the rest here, but very good quality.
The IMPs were purchased with cost the main consideration. They work well with an instrument with a good output - i.e. a SC
ProOne synth, but poorly with an instrument with lower output - i.e. a Fender Precision. Again this usage is in a live sound situation. They are passive which accounts for some of my personal experience I'm sure.
For recommendations from my experience I'd probably hype the Radials - any of their DIs actually - as they appear to be extremely well built and do the job extremely well also.