I can second
@tink1970 on the Sheraton Grand in Edinburgh. It was very nice!
IMNSHO the Club Carlson card is absolutely worth the hassle and a keeper card if you think you might go to Europe every few years. Before the Hilton Aspire, this was my favorite sock drawer card. My mom has it and does not travel like we do. She has received more value with the 40k annual card Anniversary points for her redemptions which exceeds the AF. She doesn’t mind paying $75 a year knowing she won’t need to budget for a hotel stay in Europe when she comes with us every few years.
We stayed at a Radisson Blu in Edinburgh on the Royal Mile. The location was perfect. The hotel itself was a bit dated and somewhat dark in decor. This was probably my least favorite Radisson Blu property but I’d stay there again. We are off to Scotland again later this month and have a few nights in Edinburgh at a Radisson Collection hotel that is new to us. I will post a review on the Hotel thread.
Didn’t see the original post so I’m not sure if you are looking for London, Scotland or just Europe in general. We used Marriott points to stay in London at the St. Ermin after a
DCL cruise that ended in Dover and it was amazing. We also stayed for a weekend at the Radisson Blu Edwardian Mercer Hotel when we went to see the Harry Potter play in London. It was an awesome stay! The staff was super friendly and it was in walking distance to the theater. We stayed at a Radisson Blu in Dublin which was phenomenal. I’d say it was the nicest of the Radisson properties we have experienced.
We also stayed once at Witchery by the Castle in Edinburgh. I don’t know if it is bookable with points but if so, I’d do it again. It totally appeals to my love for the unique, whimsical, dramatic and absurd. Left to my own devices, I’d stay in each one of the rooms.
@PlanePrincess rolls his eyes whenever I mention Witchery by the Castle (it’s a bit on the spendy side) but he has a tendency to do that with most of my suggestions

I ignore him and look forward to saying “I told you so” at some point in the future during said trip. Batting a thousand here with that.
Iceland, we used Hilton. We had gold status at the time thanks to the Amex Plat card (before the Aspire card existed) and were upgraded to club level which gave us club access. This saved us a ton of money on food! I always consider elite status, club access and food when deciding what points to use at what hotel if the type of vacation lends itself to that.