My recomendation would be to go with whichever hotel is cheapest. If both were the same price, then Waldorf.

I'm pretty sure my room was a renovated one at the Waldorf, certainly wasn't outdated. The room I had at the Trafalgar was bigger than the Waldorf and the bed was a king at the Trafalgar (I was told I had a queen size at the Waldorf but it looked like a double). I liked the Nespresso maker at the Trafalgar. I was travelling solo and wasn't in the room much anyway.

I liked the breakfast a lot better at the trafalgar, nice continental buffet and when I stayed there last year, diamonds could order anything they wanted off the menu. From what has been posted on FT, it appears that it is only the Cont buffet now. I didn't try going down to the restaurant and seeing if I could order a hot breakfast based on what the front desk told me and what I have seen posted on this thread.

I recieved no wine or welcome gift in my room (at the Trafalgar I only received a pack of shortbread cookies in the water) outside of the bottled water, but since I was so late arriving at the hotel and had to be up at 4:45 a.m. the next morning, I would have rather had the free room service dinner this trip over a bottle of wine.

Advantages to the Waldorf for me were the lounge from 3 to 8, was nice having the free alcohol selection from 6 to 8 and there were small finger sandwiches from 3 to 6 and I liked having access to a printer. Both hotels are in great locations, but I liked the Waldorf being closer to the Picadally line for LHR access. It is only a few minute walk to the hotel from the stop and seeing I had to be at the airport early yesterday and had a lot of luggage with me that really helped.