Staying in London
My family just stayed the past 7 days at the Marriott Marble Arch. We found the accommodations excellent, friendly service, and knowledgeable staff. During our stay we took advantage of the indoor pool and health club and while not overly spacious, it was sufficient for a 'vacation workout'. The concierge service was excellent, helping us find tickets to hard-to-see venues such as the Globe theatre.
Our room package included two buffet breakfasts each day. I strongly recommend taking advantage of this option. The food options are plentiful and includes a made-to-order omelet station. In addition to the standard English breakfast items, fruits and cereals were varied and fresh. Watching the World Cup in the bar area was great fun and included free appetizers.
The hotel is an easy walk to the Underground or Tube train system. We purchased a weeks pass and never traveled by bus or taxi. While the Arch station is not an exchange site (no connecting trains are here), this was never a problem. The longest wait for a train at any time during the week was 3 minutes. Listen for the announcements of delays when you enter the station. There are many options for getting to a location by various connecting trains, so if one is having issues you can re-route to another and not be impacted.