To me, it's a tie (which is weird coming from me because I'm a bit MFS biased, haha!). The thing about them is that while, yes, they have many similarities, I view them as two band in completely different genres. I feel like if comparing to MFS to OOR, it would be compared to OOR's harder songs since I'd say about 90% of MFS's songs are composed of screams while Taka had mentioned he's no longer going to scream any longer in his songs. The truth of it is that both bands have their good and the areas they need to improve on, and while MFS's fanbase is pretty decent, OOR does have the experience on them. They formed in 2007, I think? While MFS formed in 2011, but I think MFS will go far.
Enough rambling. lkdsjkldsf It's a tie, and I love both bands. Taka has the cleaner vocals (while Hiro's are still developing) and Hiro's screams are on point, even during their lives. Both great bands, and I reccommend them both all of the time!