Westin is grand and used to be excellent and I stayed there regularly up until 2 years ago, more recently there seems to have transitioned to large groups and the standards of service have dropped accordingly. It is a very large hotel and in my last stays it felt overcrowded (e.g. waiting 20 minutes to be seated for breakfast) so I moved on.

Santo Mauro is the best alternative for me and where I normally stay these days, although rooms can be a bit random (they are VERY different from each other, some are breathtaking, some are weird). Palacio is very nice. Circulo is at a different level in my opinion and is below the others both the rooms and spaces as well as the service (that suffers from having all food provided by a different company - good luck trying to order breakfast in the room!).

Aloft etc. cater to a different crowd, but are still great for younger kidless individuals looking for a very central location and 80s and 90s retro feel.

Breakfast in Santo Mauro and Westin is great, but different. Santo Mauro is a la carte and Westin a huge buffet. Santo Mauro breakfast outside in the garden during the spring/summer months is the best!

In terms of upgrades, Westin is the most likely to give you one (they have soooo many suites), Santo Mauro can provide the nicest upgrade in Madrid if you are lucky although in my experience the upgrades improve once you become a regular, and Palacio has some amazing suites as well. I have rarely been upgraded (in a noticeable way) at Circulo and Aloft does not do suite upgrades (all rooms are the same).