Stipe is a bigger name, and because of his seniority in the company and his well-earned status of being one of the best HWs of all time, his popularity, and to some extent his age - this is probably his last chance at the title, while Sergei will have several chances for sure as he's still young - I would like Stipe to get the nod. A battle of big-man legends, very excited for it.
If the angle you're coming from is who has the better shot of beating Jon Jones, then Sergei may be a better choice. Sergei probably even deserves it more, having fought way more recently than Stipe, and 8 Round-1 KOs in a row, I mean, come on.
But Stipe/Jones is a fight for the ages.