They’re such different players that it’s hard to say. It really depends on the makeup of the team. Pavelski was so versatile, he could play any forward position, be a key guy in both offensive or defensive situations and was a great complementary player on a top line. He couldn’t drive a line offensively as well as Kessel though.
If I need someone to carry a line that gets a bunch of offensive starts and QB a PP, I’d take Kessel. I don’t think Pavelski would have been as valuable to the Pens in 16/17 as Kessel was based on how they were set-up. Or say Kane’s role when Chicago was winning. Meanwhile if I need someone to play a tougher two-way role on a team with more offense, or next to better offensive players, and play a net-front/bumper role on the PP I’d take Pavelski. If those same 16/17 Pens were adding either a second Kessel or a Pavelski, I’d take Pavelski, as he’d probably fit better next to Sid or Malkin or even bump Bonino down.
Their careers are somewhat similar as it depends a bit on what you want. I’d say Pavelski had the better regular season career due to his longevity, but Kessel had better playoff success, and was arguably better there. That said, I think Pavelski’s playoff career can be overlooked. He has runs of 14 and 13 goals, and several where he was above a PPG in over 10 games.