Thiem is the defending champion, defeating Federer last year. So in the absence of Roger, he is rank 3, behind Djokovic and Nadal. Most of the top rank players entered this tournament so it will be interesting who will win tournament. I haven't check the odds though, but it looks like Djokovic, with the strength of his recent performance will be the favorite.
For sure, Novak Djokovic, Rafael Nadal and the defending champion will be the favourite for this year.
And then Daniil Medvedev, Stefanos Tsitsipas and Alexander Zverev. Hard to predict this early though, we might need to see their 1st and 2nd round performances before making any bets.
Also you have mentioned March 12th as the starting date of the tournament but I think its March 9 .