Stryker Sulak!
No, seriously, I wouldn't mind either way. I think that they're both good players and don't have any big skill disadvantages compared to the other. Maybe Clay is more of an overall guy and Thompson is more of a blitzer (Although Clay has been doing amazing in practice apparently).
I don't mind having either of these guys in there. Like I said, Matthews can get some pressure, but is also the perfect compliment to Kampman, a LB who you don't want in coverage to often. Thompson might fit that role as well, eventually. Like I've said before, I'd really like for him to progress into a Shaun Phillips like players. Hearing what he does in shallow zones bodes well, though.
My prediction as of this point is this : Thompson starts and will eventually be replaced by Matthews. Maybe as early as pre-season week 4, maybe as late as regular season week 8, but I really think that this kid is ready to play in the NFL already.