Very rarely did I ever use a hose. The best IMO would be to use a clay bar + soap and water on occasion. This helps easily remove bugs, tar, dirt, etc. After that, your choice of detailing spray. The only time I would you a hose was once a season, I would spray down the engine compartment with a mild engine cleaner to take care of any
oil/dirt that I couldn't get with my detailing spray/hands. Underside was always by hand, as I don't have access to a lift, so I would jack up each end and do what I could to make the underside look as good as the topside. Also, obviously you would want to get a high quality wax to make sure paint and such was looking as good as possible.
