I believe, from of our current strikers (Martial, Rashford, Ronaldo), ten Hag prefers Martial because his back to goal play is superior to the others, and if we look at his previous strikers, most, if not all, have excelled in this area, whether it be a false 9 in Tadic (tried Eriksen there first game) or a target man like Haller.
Having said that, ten Hag has played Rashford in Martial's absence, and I think it's fair to say Rashford struggles with his back to goal. I think where he gets the nod over Ronaldo is due to his dynamism and work rate.
For me, whoever we do get needs to be good at holding up the ball, especially as we have a player like Bruno as our attacking midfielder. I personally find it no coincidence that we see a better Bruno when Martial is in the team, as the two dovetail superbly. Its kind of like the partnership we saw from Kane and Alli under Poch.
If you look at the strikers ten Hag was apparently in for, i.e. Arnautovic, Kalajdzic, Sesko, etc, they are all big, strong, target men type strikers, and I believe that's the profile of striker we'll be perusing next season, or even in January depending on what happens with Ronaldo.
Alexander Mitrovic
Ivan Toney
Benjamin Sesko
Patrik Schick
Dusan Vlahovic
Tammy Abraham
Dominic Calvert-Lewin (wildcard)
May not be fancy names but the players above will give us a different option to what we currently have. Well, they'd give us similar to what Ronaldo gave us last season with better work rate and perhaps better hold and link play.
An option of Martial, Rashford and one of the players above would be a perfect blend, in my opinion, with the aforementioned two more than capable of playing with them if we were to go with two up top late on in games.