Brentford to win to keep Chelsea potentially catchable, or Chelsea to win to keep Brentford well behind or the classic "draw with lots of red cards and injuries"?
If we finish behind Brentford, it means we would not have qualified for Europe anyway. They are simply not good enough to win the number of games it would take to first catch up and then compete for European football. If they finish 11th and we finish 12th... who really gives a shit? 10th, 11th, 12th or 13th all result in the same empty stare into the abyss.
Chelsea, on the other hand, is a team we can catch and if we finish above them we're very likely going to play European football. We want one or two teams to properly slip up while we hopefully win a fair bit of games... and Chelsea slipping up against Brentford could end up very helpful.
No-brainer from me. We have nothing of importance to lose from a Brentford win. Plus it is very fun when Chelsea lose.