Originally posted by bobore Hoya HMC filters (Japan) for me on every lens.
+1... I have one on every lens I own, for protection only. When conditions allow - eg. no rain, no dirt, no grit, sand or spray blowing around, shooting indoors - or if I'm shooting toward bright lighting (inc. lunar shots, bright street lights, strong sun reflections off chrome etc.), I take the filter off whatever lens I'm using (the less there is between the lens and my subject, the better
). The rest of the time, it stays in place... The benefit - and this is a personal thing - is that I can easily clean the filter in the field with whatever cloth I have to hand (usually microfibre, but I've used my shirt tail, handkerchief, turned-out jeans pocket etc.) and not worry about having to remove any non-obvious contaminants with a blower or brush first. Only recently I managed to scratch a filter this way... not badly enough to warrant replacing, but if the scratches had been on the front element of the lens, I'd have been upset about it. With time, I've become adept at judging when the filter may result in unwanted reflections, and I balance my decision on the shooting conditions and risk of impacting an image.
I also use hoods when required, and I agree with others here that they offer great protection (plus, of course, they can play a big role in reducing flare and optimising contrast) - however, when you're shooting somewhat into the wind in a dusty / sandy / wet environment, they won't keep the front element clean - especially if it's a wide angle / normal lens (the longer tele hoods do seem a bit better in this respect so long as you're not shooting directly into the wind.
I test every UV filter I buy. Some time ago I noticed a strange effect in the bokeh on some of my images, where slightly out of focus areas had feint diagonal lines clearly visible. Testing proved the effect was caused by the Kenko UV filter fitted to the lens. I then tested my other UV filters and found several that were optically poor for one reason or another. I've never had a problem with the Hoya HMC UV(c) filters I now use, and they're also one of the best in terms of minimising unwanted reflections. In general, I notice no degradation of image quality from them - comparing with / without filter images at 1:1 magnification in Lightroom... However, I have a couple of old Tamron Adaptall lenses - a 60-300mm zoom and a 300mm prime - both of which do seem very, very slightly sharper without a filter. The difference isn't noticeable at 1:2 reproduction, but it's still worth bearing in mind.
It's an emotive and divisive subject, but so long as the pro's and con's of using UV filters (and not using them) are understood, it's down to the individual photographer to decide what works best for them
EDIT: Congratulations on your new "plastic fantastic" DA35 f/2.4... possibly my favourite lens