Were your friend willing to purchase where required, I'd advice him the Merlin TSM, new or used. They're closed, easier to drive than most Dynaudios and B&Ws. Soundwise they have one of the best mid-bass responses I've heard on dynamic 2 way monitors. But if that's not an option, I wouldn't get any Dynaudio below the Confidence C1. Most others, even the S25 Anniversary have too much mid-bass response, which in a mid sized room would be quite troublesome to handle. I would advice him to try at home before committing to purchase them. If that's advisable with any speaker, I think that's more important with Dyns and B&W.
I have listened to a couple of Triangle. Quite easy to drive, kind of "correct" but a bit in the bright side of things for my taste. I prefer Spendors, Harbeths, Merlins and even some Focals.
No experience with Linn speakers at all
Regarding B&W I agree with Dusty, they are the best selling speaker manufacturer for a reason. However I haven't really dug any of their speakers, from the almighty 800D to their affordable home cinema series. They are hard to drive, more for their impedance swings than for sensitivity. He'd need a competent 2Ohm compatible amp to drive them well. The 805 are very decent, I could probably live with them, but again, he'd better try them at his place before closing the deal.