i'd go with a desktop. vista, big 24", dual core or whatever, quick hard drive.
laptops if one part breaks you have to send it away, small keyboard, slow hard drive, to name a few disadvatanges. if you do go for a laptop i recommend a wireless keyboard and mouse.
a 13" or 15" laptop isn't worth it imo. 17" is the way to go and you can pick em up cheap, at last you can get a decent size keyboard. picked up a compaq on sale, 17" for £349. blow whatever you have left on software and beer.
i don't get the interest with netbooks, tiny screens, big premium. they're not practical for watching youtube vids let alone work on. if you don't have the strength to carry a 15" or 17" you should get out more.