I have stayed at 1 Residence Inn and 1 SB (San Jose Milpitas), 2x Candlewood suites (PHX and Turlock CA) - all on PB. I'm travelling with 3 kids so space is important to us - if the price is the same I would stay at Staybridges vs HIE/HI.
Here's my verdict:
I love the SB and CW. Got upgraded as Plat to 1 bedroom suite. The breakfast at SB was great - comparable to RI.
CW doesn't provide breakfast but in PHX there was manager reception (pizza party) - we got pizzas from Papa John and salad and cake and soda.
The main reason why I don't stay at RI is because the earning ratio - I only get 5 pts/$.
One big thing that I prefer IHG's extended stay vs Marriott: free laundry on site.