I would have to say that Torrey Smith is the better keeper. Steve Smith had a resurgence last year under the amazing rookie campaign of Cam Newton. However, he's only reached half the ammount of 100+ yard games as he achieved last year, and he has only caught one TD pass this year. As a result, his fantasy production is way down. And as a 33 year old, we may have to face the reality that we have seen the peak of Steve Smith, and it was 2011.
On the other hand there is Torrey Smith, who is 10 years younger than Steve and is poised for his "magical" third year next year. (If you haven't heard this, NFL wide receivers consider the third year in the league the year where you come into your own. I heard about this and thought it was a myth, but you can see Michael Crabtree's third year this year is better than the previous two combined. Also, the 2000 Draft Class is ususally used as an example. In that classe's third year, 6 out of 8 had their best year in their third year.) Torrey has made a name for himself this year, and continues to show he is capable of big catches in big situations. He's the guy to keep.
As far as a remaining roster position for this year, it would still be Torrey Smith even if it wasn't a keeper league.Torrey is #16 this year among WR's, and Steve Smith is #35. Torrey hit a slump in the last few games, but that will change this week vs. SD.
Plus, I'd rather have the guy on the team that actually has a (slight) playoff possibility (and will therefore be fighting) than the guy who's on the team that has no chance of a playoff birth.
Final thought: in their remaining 6 games of the year...
Steve Smith: 1 bad matchup (ATL), 4 regular matchups, and 1 favorable mathup (NO)
Torrey Smith: 2 bad matchups (PIT & CIN), 2 regular matchups, and 2 favorable matchups (WAS & NYG)
hope this helps
RB: Martin / Lynch / Lacy / Ridley / Wilson / Michael
WR: A Johnson / VJax / Gordon /Ja. Jones / Nicks / Douglas
PK: Bailey; DST: KC