We found bus service at AKL to be just fine. Think about it this way, at the end of the night, WDW can increase the number of buses running, that can't be said for the monorail. AKL is a very fun resort, easily the best value of the deluxes if you have kiddos that enjoy that sort of thing.
I haven't seen the Riviera up close but from what I have seen it looks ... nice. But like a really lower-case n, nice. Kinda bland, or not bland but just not quite Disney enough. Like if they set bedrooms up inside the California Grill. A wonderfully magical Disney restaurant but I wouldn't want to sleep there.
POR is my go-to resort. It's always a safe bet. But if you enjoy the dining plan, sometimes factoring in the cost of upgrading it, the price difference between POR and AKL is small enough to make the decision that much tougher.