Bethalize: the lack of RSS on free WP blogs is a matter of the user not putting a link, not a limit of the platform (but it is a bit confusing to add).
I have a self-hosted WP blog (actually a few), which is ultimately the most professional, in my opinion (to be fair, I do Web development for a living). Mainly because you have your own domain, and can do a ton of customization. It helps to know what you are doing though
Blogger (a Google product) is a fairly easy to use platform (no more difficult than LJ, if I recall, although I havenít used LJ for 7 years or so). It allows for a lot of customization, monetization, etc, but you can also get around pretty easily with just basic themes. It also allows you to use your own domain while still having it hosted by Blogger. (not sure on cost of that). For the average person, I almost always suggest Blogger.
Free WP is extremely easy to use and has some very cool features, but offers practically no customization and you canít monetize it. It has some good free themes, but a lot of the more customizable themes cost money, and even something as simple as changing text colors requires you buy into a payment system. I have a small blog on there, but three months in, I really wish Iíd chosen Blogger instead, and may port it over soon. I decided to try the free WP system to begin with since I am familiar with the self-hosted version, but itís really not the same except at the most basic user interface level.
As for running it on LJ, I find that is definitely more of a personal journal or niche topic site. A lot of emphasis is put on a community involvement (by the platform, I mean, not individual users), which is fine if your readers are all LJ members, but can be off-putting to non-LJ members. They also make it difficult to add RSS feeds and show ads that you donít profit from unless you become a paid member.