I unequivocally believe Vlad is the most valuable member of the Jays - when all on-field and off-field things are considered, but... yeah as far as on-field only, Springer has kinda separated himself from the pack, especially over the past month.
The top 4 are Kirk, Springer, Vlad and Bo... Kirk and Springer already above 4 fWAR and have an outside chance at 5, Vlad and Bo could both end up above 4.