Level 45: This is the chi tier.
In terms of raw math, Power Strikes will provide you with more chi than Chi Brew will. 1 extra chi every 45 seconds, to be precise. However, getting it does sacrifice the flexibility of picking when you get that chi as well as the benefit of getting some Elusive Brew stacks. Of course, the overall difference is actually not that much. Ascension is more reliant on your haste rating to provide chi, but it's real benefit is the extra slot for more chi, which allows you to have a greater stockpile of the stuff. However, that benefit is somewhat eclipsed right now due to the fact that our energy regen is severely limited. Because chi is far more valued this expansion, you're going to want to ensure that you have a healthy income of it. Unfortunately, Ascension does not allow for such. To sum everything up, go with with Power Strikes for more chi (preferable for fights where you need to purify more), Chi Brew for more Elusive Brew stacks (preferable for fights where you need to avoid more attacks rather than soak them), and Ascension if you cannot pull off the basic priority and survive.