The Rams need at least one good WR, preferably two, and of course a QB.
If you address WR first the Rams could win enough to get into the playoffs, no doubt. That plus Gurley, plus the young OL coming into its own, etc would be enough. But then our pain would change from "why can't we have a winning season" to "why are we just another speed bump for the real contenders in the playoffs." Keenum is not the guy who will turn this team into a true contender. He could QB a winning team I think, get us into the playoffs, but that's about the length of it. His real value is as a cheap bridge option until the draftee knows the offense well enough to play.
QBs drafted nowadays need transition time. The Rams need to make that move so that clock can start ticking. With a solid backup type starter who avoids mistakes, a young OL, and the best young RB in the league in place, they're in a perfect spot to offer a drafted QB a bright future. This isn't some junk team that has to rebuild, and if they take the QB this year it means he will be ready for the opener in 2019 in the new stadium, don't think for a moment that doesn't matter.
This draft is quite deep at WR. That means the Rams can get a couple good WRs to help this unit into midrounds. Also, the "we need a #1 WR" stuff is hogwash. There is no correlation between having a dominant WR and winning championships. That is more about defense and overall balance offensively. Balance on offense can be had by simply adding a couple very good matchup problems in this draft, which is very doable without touching the round 1 pick.
The real question is whether the Rams can afford to move up to get a QB and still address other needs. The answer is yes. So, given that, plus the fact that Goff in particular is the most ready to play now, means trading up for him is my preference and what I would do if I were the Rams. They are not going to find a Brees in FA. They are probably not going to find an answer in trade either, given the insanity by teams in this FA period. It's gonna have to be the draft and if they go in to it wanting a guy they think will go round 3 or 4 and some team takes him, they're screwed so they cannot risk that. Moving up is the way IMO. It's what the Rams SHOULD do.