The bus service for the DTD hotels runs on two routes. 'A Bus' and the 'B Bus'. The Hilton runs on the A Bus schedule which goes to the following properties in order:
Hilton
Holiday Inn Express
B Resort
Double Tree
The buses typically run every 30 minutes or so, usually :35 and :55 past the hour and up to 90 minutes after the parks close. Yes, the buses are crowded, though I have never seen a Disney bus that was not in peak hours and dates at the parks. One benefit is the Hilton is the first stop for pick up so the bus "should" be easy to get on and find a seat.
The bad is that you have to go to all the other properties before heading to the parks. Just adds a little more time is all. You can walk across the street to the Wyndham LBV and jump on that bus (B Bus) which only has three stops and runs the same time frame as your bus will. You can also do this coming back from the parks if your bus is not there yet. Just jump on the B Bus and get off at the Wyndham LBV and walk to the Hilton. It's right across the street.
As Grumpy92 mentioned, Since the Hilton is so close to DTD, you can get buses there and walk across the street as well. Be ready for a wait there as well if you visit now during the summer. I see a line of Disney buses sitting there waiting to get into their DTD area for a good while at times due to all the traffic of other buses as well as typical DTD traffic.
Speaking to a family the other night (this week) at The Boathouse. They said they waited on a bus in the bus queue at DTD coming from EPCOT for close to 30 minutes before getting off at DTD. So, it's a pick your poison really. I have stayed at every property on Hotel Plaza Blvd. several times and have had very few issues with bus transportation, to and from the parks.
p.s. - Not really sure why these properties are referred to as "off site" when they are in fact on Disney Property. I guess them not being "Disney Resorts" makes them off site? Oh well, just something I see a lot of I guess.