If you can afford it the Park Hyatt is WONDERFUL. I always stay there, but always am using free nights from Hyatt -- probably put in 25-30 nights there in the 10 years that it's been open -- bless Hyatt's frequent stay program. Certainly never had a problem bringing respectable "friends" back to room. If you are not into the bar scene just try cruising Shinjuku station -- the main facitility inside the ticketed area is always busy and always cruisy. The basement My City is also good. Quite a few other choices also in and around station. Should you stay at the Park (or for that matter the Century) they both have shuttle buses to Shinjuku on a fixed schedule which saves a 10-15 minute walk or $6 taxi. Feel free to email me if you want more specifics.