Just wanted to give a quick trip report having gotten back from a three night stay at the Budapest Westend. Had really amazing service as a Diamond. Was sent up to the executive lounge for check in. In the room there was a bottle of champagne (well, Hungarian sparkling wine) and a nice little desert. Much to my surprise the desert was replaced every day (but not the champagne!

).
I found the location to be great. The Castle location wins hands down for beauty, but it is sort of like staying on the Mall versus staying in Dupont Circle if you're in Washington DC -- the Castle is near many of the historical locations, but the area is kind of dead, while the Westend is a walk (or metro) to many of the sights, but closer to the action.
I actually walked everywhere and didn't find it difficult. It was about 20 minutes to St. Stephen's Basilica and maybe 30-40 minutes to the Chain bridge.
I cannot say enough about how nice the staff were. I had a problem at checkout with my rate (I booked the "Great Escape" and then ended up charging me the rate for all three nights for each of the nights) and they cleared it up immediately. The Exec Lounge staff were amazing, the front desk staff very helpful.
I am not sure if it was my rate or all Diamonds get this, but I was given the choice of either breakfast in the lounge or in the restaurant. I tried both and there is more selection (and more crowds) down in the restaurant, while the lounge is a bit classier (linen placemats versus paper). The difference in selection is not truly overwhelming, just a couple of items really, but there is a small difference.
Overall, if you're looking strictly for location, I would say the Marriott, the Intercontinental, the Sofitel, or some of the higher priced chains (Le Meridian, Four Seasons) have both Hiltons beat, but I still really enjoyed the Westend and will return there when I go back to Budapest.