Which do I rate most highly or which is realistic?
I would cross Lycett and Witts off the list - they can play in the same side as the team's #1 ruckman without much of an issue so I doubt they'd leave. Sinclair gets his hand to a lot of hitouts but they are wayward hitouts. Solid around the ground. I'd be interested for a cheap trade but not much more. He'd instantly displace Cordy and do a much, much better job than him though so that's a plus. Naismith and Nankervis are too far off senior footy for mine - if we're looking to trade for another option we'd want him to be capable soon, I think. Hickey I'm yet to be convinced on and has a worrying injury history. I like Phillips - equally capable in the ruck and around the ground. Nicholls has a lot of talent - very athletic but gets pushed/held out of ruck contests too easily - his work is very much to advantage though.
Nicholls probably costs you a decent asset; Phillips probably does also. Sinclair might be a good cheap option. I've discussed this with you before but if searching for a capable, ready-to-go ruckman who's also capable up forward, Jarrad Redden is the man to target - would cost a bit though.