Bautista is the better hitter when looking at offensive WAR and considering that he's had far fewer plate appearances in a Jays uniform. There's a chance he will pass Delgado for #1 on the list by the end of next year with ~1,300 less plate appearances.
The only way I can see Delgado being considered better:
1. The question is posed as who is the best hitter, regardless of position. So the negative positional adjustments applied to first basemen versus right fielders when calculating WAR should be excluded. Bautista would benefit from superior baserunning which would also need to be excluded.
2. Delgado performed in the steroids era with high league wide offense. Therefore it was more difficult for him to achieve an elite level of offense versus the league average compared to Bautista's output versus league average. If Delgado was transplanted to 2010, would his numbers still be the same, and thus things like wRC and oWAR be higher? He was never implicated in any steroids witch hunt so he has that in his favour, but this point is still too speculative to say for sure. Delgado's counting stats like HR and RBI are still significantly higher than Bautista's as well as most of the rate stats.
3. Delgado mashed for a long time while Bautista wasted most of his 20's being a marginal player. Bautista has achieved almost as much oWAR as Delgado in far fewer PAs, but the fact that Delgado has so many PAs in a Jays uniform in the first place speaks to his longevity of being a useful player. Bautista would have to hit at this level until age 40 to make up for his lost youth.
4. Delgado put up some useful years in other uniforms while Bautista's career outside of Toronto has been marginal. But then this goes back to considering players like Molitor, Thomas, Henderson etc.