I've been trying to get Best for this same situation. If you have good RB depth, then I'd say pull the plug. If you're betting on Best playing a full 16 games healthy, then I'd opt to stay with Wells.
ESPN, 8-Team League
QB Tom Brady, NE QB RB LeSean McCoy, Phi RB RB Darren McFadden, Oak RB RB/WR Fred Jackson, Buf RB WR Calvin Johnson, Det WR WR Steve Smith, Car WR TE Jason Witten, Dal TE D/ST Ravens, Bal D/ST K John Kasay, NO K
Best had turf toe happens to everyone. He is on the smaller side and lightning fast so he takes big hits. Beanie has also had his share of injuries and he will be pretty beat up by the end of the year. I say though its a push because its not full ppr league. But very close.
10 team ppr w big play bonuses
QB E. Manning RB C Johnson, Forte, Sproles WR Marshall, A.Brown, Decker TE Finley DEF Houston, K M.Bryant Bench: D.Brown, M.Bush, J.Rodgers, Amendola, D.Moore, Flacco
I'd take Best over Wells, and I don't think it's that close. Sure I have some concern about Best staying healthy, but Wells isn't exactly an iron man himself. Best is on a better offense, and is the better player. The fact that it's ppr makes Best even better. Get Best!!