The penalty may have been a joke decision, from the linesman's POV it was an obvious pull even if Walcott embellished it, but even then he's much more rash in his defending than Jones and Smalling are. That's not because his positioning is poor, because positioning and reading of the game are his main assets IMO, but because he is too slow to catch up with an attacker that gets past him. He could easily have had a second yellow against Spurs for one particular "tactical foul" when he already was on a yellow. That doesn't take away from the fact that the first yellow IMO was bollocks, but the point still stands.
I've said this for a long time, but defenders who often resort to sliding tackles are doing so because either a) they're out of position* or b) because they're too slow to catch up with the attacker. Evans has always been much more about sliding tackles than Smalling has, and also from what I've seen of Jones.
Now, this is a lot of personal opinion here, but I'd take a non-sliding defender (Rio, Smalling) over a gung-ho sliding defender (Puyol, Micah Richards) ten times out of ten. That's why I can't see Evans being more than fifth choice CB at United. I do however have to say that I've found his recent form extremely refreshing and shows good mental strength to bounce back like that from an awful last season.
* For example Jones vs. Bale where he was out of position but managed to recover in time to put the sliding tackle in. What sets this apart from the example is that he didn't slide at the player in order to concede a foul, but that he slid away from the player in order to prevent the cross from coming in.
Whatever the outcome, it's a bit ridiculous that we're talking about such talented players in terms of who's fifth choice centre back for us, but in an awesome way.