Clark was solid and has been good all year. I'm probably biased as a Newcastle fan but he's always done great for the club and his new deal reflects that.
If he's fit then he's our best centre back. It's a no brainer to start him with the injury and form problems to consider.
It's an unproven duo but I'd go for O'Shea and Clark. With Doherty/Coleman and Stevens, then that's a legit Premier League back 4.