I prefer PA over Peninsula esp if you are platinum - I find the Peninsula to be tired. And I don't like the location. Service is good but nothing spectacular. I only stayed at Peninsula once and was quite surprised (negatively) as it is always ranked so highly in Travel and Leisure. It was not a bad stay but nothing superlative and there didn't seem to be much of anything within walking distance. I am a walker and that was negative for me.
I stayed a few months ago at Mandarin Oriental (hadn't be there in 10 plus years) and still loved it. A little tired in parts but the service was just incredible. Seriously incredible. So if you want the river views and are chain agnostic, I would choose MO over Peninsula unless rates are really much cheaper at Peninsula.
Royal Orchid is a great deal on river too if you want to stay with Marriott, though definitely not luxury. But so cheap. ANd I have gotten a suite every time I have stayed there. But I still prefer PA.