From a welsh perspective (I don't have time to watch more games, other than the premiership highlights), I think the following deserve to be mentioned:
AWJ at lock. Been exceptional as always for the O's.
Tipuric/James Davies. Both been very good for their regions. Davies did come up a little short in Europe (in a struggling side though), and has been injured recently though. Tips is pure class.
Dan Biggar. Like him or not, he's effective.
Dan Evans. Don't think he's international standard, but he's still been quality for the O's this season.
Surely there'd have to be a fair number of Sarries and Wasps players in there. Sarries are unbeaten in all competitions, and Wasps gave 2 former champions battering's in Europe.