I decided to book the Skyline for my last overnight this past Sunday to see the difference between the two hotels for myself. Still a great rate at 59GBP but 10GBP more than I could have had the Sheraton Heathrow for.
Transportation, very nice option at the Skyline is to just go to the central bus station stand between stand 19 and 20 and grab the first of many buses that come along. The bus stops are better situation at the Skyline also IMO.
The Skyline has a much nicer lobby and common area than the Heathrow. There was no line at check in and only saw a few people waiting at any given time. Staff was very nice.
We did eat at the Sports bar and it was pretty good and had decent prices. It is bar food with the exception of a special curry menu specials listed and since the cooks are Indian my wife thought it might be pretty good and it was. My food was also good as was the service. I really wish the Italian restaurant was open as that was much more to our liking but understand the closure.
As a Plat I was upgraded to a 3rd floor exec room and the room was really nice and definitely larger than the Heathrow. The bathroom was much nicer and larger at the Skyline than the Sheraton Heathrow.
Exec lounge was actually much busier than I expected on a Sunday evening. It is very nice and had some decent hot food offerings. I thought the wine they served sucked though. The free wi-fi in the lounge along with a couple of workstations available for use is better than the Sheraton Heathrow which only has a couple of old crappy laptops nailed down to a counter top for use. Breakfast in the lounge was good and the staff did a very good job.
All in all, the Skyline is a much better property in about every way. Having said that....depending on price and length of stay I would not hesitate to stay at the Heathrow especially since me and my wife like the Chinese restaurant down the streat from the Heathrow.