I'd definately do either self catering or B&B if there's a good deal. With a large group of mates in Self Catering, you can share 3 or 4 to a room and keep the costs down lower than in a hotel. Make sure you go for apartments with a good pool area etc as you won't always fancy walking down to the beach (esp. with a bit of a rough head
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I really wouldn't consider All Inc as a group of mates your age will not want to stay around the hotel all day and night with the same people, pay for a decent apartment and get out and about and do stuff (and no worrying about getting served
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Resorts that might appeal based on what you have said about good nightlife but not OTT and considering budget... all my own opinion and based on places i've been.
Kardamena on Kos, small compact resort, good restaurants, loads of bars around the square and down 'bar st' and 2 clubs. Sort of young & lively mixed with families and couples, all music indoors at midnight. Went in 2008 and would go back but it is the smallest of the resorts I'm listing.
Stalis on Crete, long & thin resort stretching along beach rd, loads of good bars & restaurant, great beach, no real clubs but only 3-4 € in a taxi into Malia if you fancy a mad one. Been here twice and love it.
Faliraki on Rhodes, bigger resort than Kardamena or Stalis with more going on. Good bars and clubs and good beach. Not as mad as it was 10 years ago, I went in 2006 and there was a real mix of couples and families as well as young groups. Make sure your accomodation is down near the beach here as there are alot of apartments that are a LONG walk down to beach/town!
I wouldn't rule out Laganas on Zante as it's got a great beach and cracking nightlife - but I've not been since 2005 and I have heard mixed reports recently???? I am going to Kalamaki in a couple of weeks which is next resort along the beach and I will probably venture into Lags a few times so I'll see !
Ayia Napa - Bigger resort and i find it a bit more expensive than the greek islands but.... the beaches are superb and the bars are ace.... I went 2008 & 2009 and I didn't find it too OTT whatsoever, nice restaurants and bars away from the Square if you want a chilled one.
San Antonio bay, Ibiza - Only gonna mention Ibiza cos I love the place so much and can't stay away for more than a year or two. Depsite the media it is actually a beautiful island and only a few areas are full of bars/clubs. The Bay area is about 30-45 minute walk from the town or €2.5 each in a water taxi. Loads of bars and restaurants around the bay. It is a lot more expensive than Greece/Cyprus (we paid €17 for sunbeds in Ibiza last August, having paid €7 on Nissi Beach in June. We spent about 40% more in 2 weeks in Ibiza than 2 weeks in Ayia Napa!... did do a couple of clubs though and 2-3 really good restaurants
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Kavos - Urrggghhhh.... NO! Filthy and full of really chavvy, chavs.... and I went there aged 23 with group of lads. Nite life was good and we had a good time but just found it too rough.