I have a Stihl pole saw, has a 8 foot reach. Can't remember the exact model, but the arm doesn't extend. It has a 4-cycle gas engine, very easy to start, and the bar is 12". It has a LOT of power for its size, I have cut limbs almost as thick as the bar is long, didn't slow it down at all. It is much quieter and doesn't use as much gas as the 2-stroke engine in my weedeater, which is a smaller engine. I have a lot of trees around my property, so I could justify the $400+ price, knowing it would get a lot of use. If I had to do it again, though, I would have stretched the budget and got the next one up, which has the extendable boom to 12'. Seems like no matter how long it is, the limb you want to cut the worst is always just out of reach.
Echo also makes a very nice pole saw, pretty much on par with the Stihl in terms of what it will do. Prices vary among dealers, but are maybe a bit less expensive than the Stihl.
One word about the 4-stroke engine. It still requires a gas-oil mix like a 2-stroke; mine uses 50:1 as do most newer ones. The engines burn cleaner than 2-strokes, and most manufacturers are phasing the 2-strokes out in favor of them. I think 4-stokes are required now in California for all utility engines.
One of the smaller ones, like the Ryobi, should be okay for occasional use and for branches no larger than your arm. I don't have any electric lawn implements, I have to go much further than I have extension cords for, and the long cords will have voltage drops (more than 50') that make the motor draw more current and heat up (shortens the motor life). You'd have to have a cord larger than 12 ga. wire to go out past 100 feet without problems, and that would be heavy and very expensive.