Both are nice players to have as your 3rd WR, so this is as "first world problems" as fantasy football gets. Last season they finished WR15 and WR16 in
PPG (that includes OBJ and his four games at WR3). So I don't know why you'd want to move one of them. If the market isn't hot for either one, I'd keep the extra guy as an injury contingency plan or flex. Personally, I prefer Marvin. He's a bit younger (1.6 years) and has room to grow in that he only saw 107 targets last year. He would only need a mild increase in targets to sneak into the low-end WR1 range. He did accomplish his high PPG via 9 TDs, but being both the deep threat and the best jump ball WR on a team likely to throw 30 TDs, it should be safe to project 8 for him.
Tate is riskier due to the contract, but I would expect the Lions to extend him. They've got a good thing going with that duo and he's not old enough to kick to the curb, as long as they don't have to overpay market value for him. The free agent market did get a little crazy this past offseason, so Tate might want to test the market.
Like you, I'm not sold on Golladay at all. He was a preseason hype darling that had two touchdowns on 7 targets in week 1. The perfect storm. He's still riding that wave, but he's just an overpriced flyer, IMO. I'd be shopping him hard if I owned him. But with a lack of a legitimate TE, there should be some spare targets sitting around this year that he might get.
