I can tell you a little:
- I would say seamless, see 2.
Do-it-yourself is certainly cheaper if you have the expertise, but I don’t. I was afraid if I didn’t install it properly that it’d just be more trouble later. Gutters installed improperly don’t just fail to keep water from dripping on your driveway, they can also cause water to back up under your roof and into your house.
The seamless also has a warranty. (15 years, I believe, in our case) Cheaper in the long run, I thought. Plus it wasn’t me up on the goddam roof.
- Seamless gutters are just that: one long piece to fit all the way across without a joint in the middle, a considerable weak spot. (Of course there are seams at the ends and corners).
They can only be installed professionally, because they are made to order right on the site. They take a big roll of flat metal, and stick it through a machine that crimps it into the gutter shape. Then cut it off in the exact length they need.
- 1 story house too: we had one long run on the long side of the house, and two runs with lots of corners that had to fit around porches. IIRC, it was a bit over $500. This is Wisconsin, so prices may be different where you are. Although the weather is about the same!
We have leaf troubles. We usually clean them out in fall after the leaves are all down. I have a long metal wand with a curved end that fits on the garden hose, plus a tool like a bent-over rake on a pole. I just get up on the stepladder and blast/scrape 'em out. (I wear a rain poncho; a lot of gunk can splash down). I have to make sure I blast out the drainpipes too.
I myself would be interested if anyone has experience with those screens or covers that are supposed to keep leaves out. Do they really work? In a heavy rain, wouldn’t the water just gush right over them? What about snow?