I would recomend HBO - definitely more mainsteam hit movies in HD, and I love their original programming, which is also in HD. Plus, if you like boxing, HBO usually has the upper hand at contacting for the better fights. For me though Deadwood, The Sopranos, Rome, Entourage, Big Love, The Wire (which hasn't been HD, but still one of the best shows around), and all the other original programming they keep putting out is what keeps me paying the monthly fee. I LOVE the HBO shows.
If you want more kid friendly movies, go with Starz. They must have a deal with Disney because they have show Pirates of the Carribean, Cars, and CHicken Little. I also have Starz and thinks it is pretty good.
If you like soft porn, go with Skinimax, urrr Cinemax. Actually, they have a lot of the same movies as HBO, just no sports and original series, plus plenty of adult entertainment at night. I think Time Warner owns both Cine and HBO. I don't sub to Cine but from the looks of the program guide it has a good variety of movies.
I did have Showtime for a while and I would have to give it a so-so rating. The movies are definitely sub par compared to Starz or HBO, and the original series haven't caught my interest. I tried to watch both Weeds and Jeffery(? is that the name) and they just didn't do much for me. I did like Penn and Teller though. For boxing they do do a good job, and most fights were HD. The movie selection was the killer for me. Seems like they had a lot of very average movies and B-movies. I would go through the entire week to set up recordings and find nothing worth using my hard drive space.
If I haven't tired you out yet, her is my suggestion. First, get HBO. bring up the list uf HD channels and get it so all 4 of the movie channels are on the list. Then scroll through a week of programming and take note of what movies and or shows you would watch or record from each channel. A one week survey should give you a good idea of what channel you should get.