I don't really have a favourite as such but there's a few that stand out above the crowd.
Pretty much any den I made in the bracken near our farm when I was a kid was accompanied by the sounds of a Skylark scolding me for being somewhere near its home.
We used to get Curlews up there so its call reminds me of that time also.
Robins look so little and nice but are such stroppy little gits when it comes to keeping other birds away that I can't stop liking them.
Got a mate who had a Wrens nest just in the eaves of his garage a few years ago, then his garage burnt down so we built another. We made a little area sort of a shelf in the eaves again in the hope that the wren would come back and although I've not seen it yet he mentioned that it has.
I always like seeing Dippers, dipping in and out of mountain streams in their little dinnerjacket.
One site I was roofing on we had long steel girders at the roof peak, they had a timber in the web and the roof spars joined to that. Someone had to nail the spars at the peak.
This was all a good height above ground and somehow I doubt the HSE would have approved. No fall arrest bean bags, no catch nets either.
Anyway one day I was ambling across the peak girder (which was maybe six inches wide and twelve or so foot long, maybe fifteen foot above the first floor joists which didn't have a floor on it so that's maybe another nine foot down to the concrete floor making something like 24 foot fall possible) with a nailgun in one hand, a handsaw in the other and my mate informed me that there was no less than ten buzzards circling above me.
In reality I know they were just using the thermals to gain height for a foray into the surrounding countryside but it did look a bit like they were just keeping an hungry eye out just in case the numpty below them slipped and broke his head.
There's something I particularly like about Cormorants as well, if there's ever a bird that looks like its been around since shortly after the dinosaurs its those. Wings outstretched as they dry them out and looking like something that time forgot.
Another is the Kingfisher, upto the age of about 27 or so I had never even seen one. Out cycling with a lad I lived in the same house as he stopped at a bridge on the way and said that a Kingfisher often alights on a branch by the waterside. At this point I was thinking to myself that as I've never seen one yet its pretty unlikely that its going to turn up right now.
Thirty or so seconds later a iridescent gleaming Kingfisher lands exactly on that branch and I perked up a bit. Another five to ten seconds later another joined it and they promptly started mating so I was very glad that the lad I know had stopped then. Maybe moving about all the time isn't the best thing and its often worth just taking a short time out to appreciate what's happening around me.
Hell, after years hating them when we had a hillfarm with lots of sheep on there but then moving out I'm even starting to like Carrion Crows. Resourceful, sleek, and bright. All needed for the balance of our environment.