Where to start...
I had a pair of k2 darko. Quality boots, though I ended up with some stiffer thraxis for this season. I would call the darko medium, but as with boards, depends on your weight. For me at 200 lbs, they were softer than I like.
As to size, I can tell you that k2 fits tighter on the heel and looser on the forefoot then burton. I have a slightly wide foot, and the k2 works well for me. I do use aftermarket insoles because I have a high arch, but that would be needed for any brand really.
If your toes are smashed into the front of the boot, they are top small. I wear a 10.5 street shoe. 10 hockey skate, depends on brand. Bought my first k2 boots size 10, expected them to pack out...they didn't. I ended up wearing very thin socks, which did help, but never was quite right. Went from 10 to 10.5 and wow!
Keep in mind that k2 has the inner liner boa, which lets you dial in the heel clamp and fit VERY well. I would recommend that you get a pair that allows your toes to just barely touch the end once your all laced up. If there's toe smashing going on after lacing, they are too small.