At the start of the year, I tend to go for a full clip, except for head and legs - legs stay on for protection from mud, and head because that's just too damn complicated to clip. As it gets colder, I go for some kind of over-enthusiastic Irish - straight-ish line from withers to stifle, with legs and head still left on. Basically, taking off the bits where she gets sweaty. Once it starts to get warmer again, I go back to full-clip-except-legs-and-head. And then, once it's dry enough, I clip everything, including legs, and my feral hairy beast is back to being a sleek, smart cob.
I tried to leave her unclipped and unrugged the first winter I had her but, oh, boy, she's a yak. She was getting sweaty just naked in her field, and inevitably came in too wet and muddy to ride. So now she's clipped and rugged and I can actually ride her.