Favorite lounge at LHR?

I have a three hour layover next week at LHR in Terminal 5 and then a three hour layover the week after in Terminal 3. I've made this trip plenty of times and always give myself three or more hours due to having to change terminals at Heathrow. But every time I make this trip I always end up frequenting the same lounge, so I'm interested in your opinion and if you have any recommendations for something different and/or better? Ideally I'm looking for a comfortable and quiet lounge, decent food, and a shower if possible. A place to nap would be nice but not necessary.

I know at the end of the day it's just an airport lounge, how good can it be, right? But, I thought I'd see if I'm missing out on something better. For example, I'd be bummed if I was hitting the Admirals Club at JFK while not knowing about Chelsea or Soho Lounge.

I'll be flying business, I'm OneWorld Emerald, and I have the Amex Platinum card so I should be able to access almost all of the available OneWorld / Centurion / Priority Pass lounges.

In Terminal 5 I usually go to the "British Airways First Lounge" and in Terminal 3 the "British Airways Galleries First Lounge"