Feel free to do what you like, of course. :) I honestly am not sure I could single out one of the services as better than the others, and I’ve used them all to varying degrees. I just had some thoughts about my experiences you might find helpful..
Honestly, the big names in blogging like Blogger, Tumblr, and Wordpress have pretty lax rules, as far as I can tell. My first blog was on Blogger, starting in 2003. I posted my share of cursing, which has been no big deal under a normal, non-adult designation. I have seen plenty of adult blogs on Blogger, as well. With pictures, videos, writing – all explicit. When setting up the blog, you can choose to designate it as ‘adult’, which puts a warning about adult content before someone gets to the main part of your site.
Tumblr and Wordpress, I have more limited experience with. The Wordpress blogs I’ve seen have been by people pretty serious about writing/blogging. Can’t say I’ve seen any adult WP blogs. Tumblr, I haven’t quite figured it out yet. I do have a Tumblr blog because it was very easy to do the things I wanted to do (kind of like a virtual scrapbook of randomness). I’m not too sure about the demographic, though.. it does seem to be quite a lot of very young people using it and most people don’t post a lot of actual text content, from what I’ve seen.
Each has their pros and cons in terms of useability, features, themes, customization. Blogger is a bit clunky, but pretty easy to use, plus they’ve updated the themes and added many levels of customization, so you’re not stuck with a stock theme. WP is a bit more elegant, I seem to remember. Tumblr.. well.. if you guys saw how many “How do I…. with my Tumblr” questions we get, you might think Tumblr isn’t as user-friendly as the others.
In terms of “rules”, I think they only care if you’re posting highly offensive or illegal material or trying to host a site for spam, selling porn, and whatnot. So, blogging about how disturbing pedophilia is is one thing (and acceptable, I’d assume), but blogging about how to go about it, posting kiddie pics, or stuff like that would likely get you banned in a heartbeat.