You could really do both bonuses... 36 nights (3 nights/week x 4 weeks/month x 3 months?) would get you the marriott megabonus plus the PC quarterly stay bonus.

The better question is what the points are actually worth. In general, Marriott points are worth far more than PC points and far, far more than Hilton points.

My personal redemption values are:
Marriott = 1.05 cents
PC = 0.43 cents
Hilton = 0.26 cents

It has to be quite a bonus to get me away from Marriott.

Have you considered saving up for a travel package reward? With your stay pattern, you should be able to get there in 2 years. That's an incredible award to snag.

You would also do well, if you are US-based, to think about using a branded hotel credit card, no matter which chain.

Regardless of your recent customer service issues, there is a lot to recommend Marriott over other chains...