I'd lean towards Garp still. Not gonna take much from Sengoku holding down Garp, since Sengoku is his senior in rank. It's not a fight, any more than Nami holding Sanji back would be a fight. Not gonna assume Sengoku's lack of feats means he's weak either, considering how little he's been in the series and his role in the Marines, but that's besides the point.
I think Garp is probably somewhere equal or just below the marineford admirals. The likes of Marco were able to make the admirals give them their attention, but still seemed to be weaker than them. Luffy barely defeated Katakuri who might well not be as strong as WB's top commanders and Luffy from what I've heard only beat Katakuri because Katakuri held back due to respecting Luffy.