At the moment? Not super clear, I'd like to at least let Madrid go by before I start predicting, but for now:
1. Alcaraz
2. Djokovic
3. Nadal
4. Tsitsipas, I guess?
Explanations:
1. Very decent sunshine double, did not play MC to shake my faith.
2. Despite a bad performance in MC, a very solid choice, assuming he can play into top form in the coming tournaments. Because of that assumption, I rate him lower.
3. He's up here because of his 14 titles. You can never count him out at RG, as I've seen quite literally almost every single year for the last 18. However, his injury concerns keep pushing back his return date and he's never had a start of the season as bad as this one. He'll have a poor seeding by his standards, and we don't even know if he'll be well enough to play any warm up events despite people saying he'll be in Madrid. If he's ready he's #1 through and through. If he's not ready to come back, we'll see what happens.
4. It'd be between him, Rune, and Sinner. Tsitsipas is the smart "also-ran" choice. AO finalist, former RG finalist, has made 6 slam SFs so far, won 2 clay Masters, and made all the clay M1000 SFs last year. The dark horses are Rune and Sinner - their level of play could produce some great tennis, but they're not the most consistent or experienced about it. I think they're more likely to win against a strong opponent in the final, but Tsitsipas would be likelier to make the late stages.
After them I'd probably have Ruud (for similar reasons to Tsitsipas) and Rublev (because a M1000 on clay is not nothing, maybe he's finally got it right.)