I had a quick 1-night stay at Delta Whistler sandwiched between a stay at Hilton and another one at Westin which allowed me to compare these three hotels in Whistler.  It was my first stay ever at a Delta hotel brand anywhere so I was not sure what to expect.  I found a BRG on a flexible rate to bring the cost down from 332 CAD to 187 CAD which I was pleased with.  I am surprised by the comments earlier in this thread noting that BRG is not possible with Delta.  It is hard to argue with the footnote from the link posted by @icebox425 which clearly says Delta is excluded, but real life experience tells me otherwise.  

Room

I had booked a 1-bedroom suite and got upgraded to the 1-bedroom suite with mountain view.  The price difference between the two is quite modest ($20 CAD) so not much of a Platinum upgrade.  They could have upgraded me to a 2-bedroom suite which was available at time of check-in but I would not have had much of a use for it so I did not mind.  The suite has a full kitchen, plus a small round dining table.  The living room has a sofa bed along with a working desk right under a very large screen TV and a fireplace.  The furniture is fairly recent and in good condition; the room has a nice home feel to it. The balcony is bigger than at Hilton but it feels like a bunker because of the walls on each side, the ceiling above, plus the vent on the wall.  It was not a nice place to go out to enjoy some sun.  Because the patio door is quite small, similar to Hilton there is not as much natural light reaching the kitchen but the room at Delta being smaller, it is not as much of an issue.  The windows are much larger in the bedroom and the views nicer from there than from the living room.  The bathroom has two doors and you can access it via the kitchen or the bedroom.  The shower is in the bathtub, unlike Westin which has a stand-alone shower.  Otherwise the bathroom is quite nice.  The bedroom is not very large, but it is larger than the tiny bedroom in the Westin suite.  The closet in the kitchen contains a washer and dryer which is convenient for people staying in Whistler for an extended period of time.  Finally, the air conditioning system is central so more modern, less noisy, and overall it works better than at Hilton.  

Gym

I stopped by the fitness gym to check it out but I did not use the equipment.  Everything is fairly new but the gym is small for a hotel that size.  There was only one stationary bike, one elliptical, two treadmills, and some free weights.  The gym is next to a pool which was very fairly busy with several guests. 

Dining

Being uneducated about the Delta brand and not having done homework, I did not know about breakfast here and found out that you get nothing at all, which was a bit surprising.  I thought Marriott was rolling out free breakfast to all Platinum guests at most brands including Delta, but this Delta hotel does not seem to be part of it.  At the moment Delta is not on par with Hilton and Westin which both offer free breakfast to elites which is worth $50-70 CAD for a couple.

Location

The Delta hotel is more centrally located in Whistler than Westin and Hilton are.  There are lots of restaurants and bars right outside the hotel.  However Whistler is quite compact so personally I do not see it as a major advantage.  Some people might actually argue the opposite because if you go during the winter it would be a longer walk from Delta to the ski lifts which are much closer to Hilton and Westin than from Delta.

Service

I did not stay at this hotel for very long, and not having a restaurant I did not have much interaction with staff.  However I would note that Delta contacted me by email in advance of my stay, unlike Hilton and Westin, and even responded when I sent them a quick answer.  The manager with whom I exchanged e-mails also came to greet me at check-in.  I was also offered to use their shuttle bus for my transfer to Westin upon check-out which was a nice gesture.  I felt more positive about service at Delta than Hilton. 

Overall

Overall I was pleased by the quality of the room and I rank Delta slightly ahead of Hilton for the room I got at both hotels even though you get more space at Hilton.  However I should note that I did not book at suite at Hilton unlike Delta so it’s not entirely a fair comparison.  If I compare with Westin vs Delta, the room is a bit better at Westin in part due to the bathroom, the balcony, and the view / natural light in the living room. In addition you get free breakfast at Westin but not at Delta so in the future I would be willing to pay a premium price for Westin over Delta.   I would return to Delta if the savings were significant enough but if money is not an issue I would recommend Marriott/Starwood Plats to pick Westin.  Delta needs to up its game in terms of Platinum treatment.