I do a ton of guest blogging. Most of my experiences with it is positive. I is a slow process to write unique content and to find a high quality site to post it on but the links are great and help a lot.
Some negatives - some blog owners will be extremely picky and send back for tons of revisions, but that does not happen often. Also have some sites that shut down after you write for them.
I normally have 1 or 2 links per article. Maybe one in context (if applicable) and one in a bio line. I will generally do 2 links if I can get it to work for 2 different sites of a similar niche.
I do not check PR but I do check domain authority and backlinks to make sure its a high quality site.