As an enthusiast who also has to drive these things...

Favourites would consist of Omnicities, Volvo B9/10 varieties and ADL E300/400s - the Omnicities are just superb vehicles all round and although they feel massive when you're driving them, when looked after properly they perform faultlessly. The one I had yesterday whilst on service 5A between Middlesbrough and Brotton worked superbly even in the most challenging conditions I've ever driven in (bar driving a MAN in a few inches of snow on my last day at Stagecoach!), 4659 just kept cracking on even though the floods were getting worse as the afternoon went on.
Volvo B10B/M were what I trained on and they were also superbly capable machines at home doing absolutely anything. They still battle on on one of the most demanding routes in the Lakes (the 505 between Ambleside and Coniston) and its hard to see what can possibly replace them. B10BLEs are just the low floor equivalent of these heavy duty, ultra reliable machines... They're equally at home on express work as they are pottering around town all day (which is why their performance on the X7 has surprised me).
Volvo B9TL deckers are also very capable machines and far more reliable than their sister 7 litre machines. I first rode on these with First in Sheffield and they've quickly grown on me and I am pleased to see GNE investing in them now, they should last far longer than the B7s.
My liking of Enviro 300/400s comes from my time driving them in London for Stagecoach at the Paralympics which I think was one of the best times of my (admittedly short) driving career and something I was extremely pleased to get chosen to be part of! I spent the majority of the time there driving 5-a-side (blind) football teams between the Olympic Park and their venues, be it training or competitive). I got to drive a few E300s whilst training (route learning) and also when we were picking them up from storage after they had been converted inside. The difference between the ADL E300s and the MAN versions I was driving at Stockton was amazing!
An honourable mention for the Pulsars must be made as they are lovely buses to drive but you get the feeling they're very cheaply made and reliability will fall off a proverbial cliff at some point. The Cadets at Stockton are reaching that stage now, though they too are superbly suited to many of Arrivas routes and many have been at Stockton their entire lives and they'll be hugely missed by everyone when they're retired next year.

As for my dislike list, I'm afraid stuff like Optare Metroriders and the MANs at Stagecoach go in here, I spent two years driving primarily the ALX300 bodied MANs and they were ok but very boring buses to be honest, not superbly reliable either, the 18.240 chassis under the Enviro 300 bodied machines used on the 36 was quite frankly awful and they struggle to keep them on the road!
There's not much else I have a strong dislike for, all buses have + points and - points and it very much depends what routes they're used on as sometimes they're clearly not suited, much like the E400s at Whitby used on X93. Clearly unsuitable buses yet they're on a crusade to try and make them fit. The Omnicities on the 685 is another example of this. GNE using Citaro bendies from London on the 58 is a great example, the buses chosen were clearly not upto the demanding route. How many odd workings are seen on there everyday and this is despite chopping the frequency to Hadrian Park and therefore reducing the PVR required yet they still can't cover the PVR with Citaros! This is despite the Streetlite demo having its own diagram too...