I think you just have to pick your club, pick your night there carefully and pick the time you choose to go. There's not a single club in Ibiza (or London) that I'd spend the whole night in... and there are plenty of big events with DJs I'd like to see but decided against it on account of the setting and likely dominance of a less than amenable atmosphere, even with the best will in the world.
The mood and crowd in some clubs can change a lot over the course of a night and through the Season. For me that sometimes means waiting till late or leaving early and moving on. It's not always predictable but if you go out often enough patterns do emerge - and they're different out there to what you get at home.
If you've not the luxury of getting to grips with things by repeat visits then best option is to take your best shot and go enjoy yourself, whoever is there. If you really can't then you need to do your homework and ask people honestly who know for best chance and then go with open heart and open mind. Steer clear of 'marketing factory' nights likely to be full of 'sightseers' in early hours. They are often all gone home by half three to 4am as they get bored. Plenty of free places open to keep you busy till then ! I've happily gone to Privilege / Amnesia as late as 5am in August and still found it worthwhile and a great night with really good crowds.
A disco nap between 11pm and 1-2am can work wonders too if you can't be bothered to go out over those preliminary hours. Get up, few bevvies and off you go with enough energy to carry on and get a decent day in when you're kicked out in the morning. Ibiza clubbing is a different beast to back home. So if you're really serious about managing your crowd exposure then there are ways round it - but sometimes you do need to be flexible and accept that you can't have everything perfect all the time.
As far as UK is concerned, I've not been clubbing since September. The London scene got so underwhelming I really couldn't be bothered to put myself through it. Largely on account of atmosphere, and crowds. And just too much time and money travelling back and forth for a smaller party now and again. In Ibiza everything is on your doorstep, masses to choose from, even ordinarily annoying people in high spirits. That's one of the great things about its nightlife. Take it for what it is - or just leave it. In the end, people getting fed up around other people when out for the night = net negative contribution. So if you think that's where things are headed then don't go out and get some sleep instead ! You're doing yourself and everyone else a favour. Plenty of other things to enjoy on the island and elsewhere.
Oh - and the clubbing atmosphere changes every year. I stopped going to DC-10 couple of years back and had taken breaks from it before. Amnesia and Privilege even more so. But last year had great nights at both Vista Room and Amnesia (though Music On for me was a total disaster - worst crowd I saw the whole Season). Space was amazing every night except one We Love (which was average)... and Sankeys was great too. Like some above I think the club that'll change most this year is Sankeys. Reckon it's entering a 'transition' phase which won't be net positive - but you never know. However Pacha may get better, Vista Room is on the ascent, Space will have some amazing nights and there will be great parties at Sirocco and no doubt other beach club venues. Will just have to see where the different crowds choose to go - and the atmosphere that suits each person will be there for the choosing. Every Season takes its own shape. Just go with the flow and see what happens... and if you really don't like the crowd of a night then take it on the chin and move on somewhere else !