It's certainly risky to go for Chase given that his current form is wildly inconsistent and he hasn't really been playing as part of a structured attacking system.
I do think Chase is a very talented player, but his inconsistencies during games would make me think twice given that he's almost certainly going to cost a lot.
The current Wigan system works very well using two halfbacks as traditional playmakers, with both occasionally running with the ball when they get the chance. I'd say that favours a combination of Powell and Smith more than a combination of Chase and Smith; but the latter would certainly be much better on paper.
There's a lot of guesswork involved obviously, but I'd say Chase would be a bigger 'project' than Smith would be.
Sarginson would be a very good signing although I wouldn't make too much of his versatility. His attacking play is sublime for a young player but his defence when playing at centre was absolutely appalling.
If the club did manage to sign him and intended to play him as a halfback long term I'd be worried about using him as a stand in centre. Consistency is usually what improves the defence of a young centre I'd guess that it's unlikely that he'd get that.
Stand off and fullback seem like Sarginson's best positions from what I've seen.