I take anything with a reg' on it although I do normally just chase bizjets/props and military transports with the rest seen 'as and when'. However, I don't do "dot spotting", I prefer to see them up close and personal.
I did go through a period of taking just airliners, bizjets, bizprops and militay transports but as types such as the PC12, TBM700 and now VLJ's became more popular, it seemed a waste of time visiting places such as Goodwood, Fairoaks, Blackbushe etc just for a PC12 or a TBM700 so I ended up writing everything down again. (although I may end up regretting that decision now Gliders have been given "proper" G- reg's!)

Martin