Depends on you and the code backing your app so all I can really say is that Cloudflare's free tier is quite generous and Vercel can (not necessarily will!) bankrupt you if you're not making money with your app. The problem is that switching isn't free, even in today's AI assisted way, so you have to balance the opportunity cost to port to their platform. (Rhetorical) What other tasks are on your to-do that you aren't going to be working on while you work on porting to Cloudflare?

My take: Choose Cloudflare for cost savings; choose Vercel for convenience with Next.js