Let's jugde them both again once they are updated. I feel in my guts that these updates won't change those cars but completely transform them.
Right now I agree that Marussia is a bit more enjoyable to drive however both still suffer from major issues. That's why it's impossible to have a grin while driving them. It's always "serious face" time when I'm on board with them.
My whole sim racing journey which is just over a year short of decade now, I've been driving OW cars, mostly F1 cars from different periods. Lot's of them post 2005 period. I had some time with GT cars prior to rF2 but never really sunk into them. It was rF2 which brought GT cars into my heart. Tintops are now my cars of choice. However I would lie if I said that I don't miss driving OW cars with a grin on my face. I really do miss it. However right now my time with for example FISI comes down to making setups, practicing, doing some tests. Always with a serious, focused face. I really hope that I will be able to drive them again and go WOW and laugh uncontrollably.
However if I had to place my vote on sth it would be hard for me. There simply isn't a car that I didn't drive and didn't like anything in it. Every car gives me joy and frustration while driving them. Some more, some less. But still I very much like them all for what they represent. GT1, 2, 3, 4 and GTE (GTD too Miro, don't worry

) are the most used for me.