1, 3, 6 links are useful. Rest all are against Google guidelines and should be avoided.
2, 4 and 7 are all against Google guidelines and your website may suffer a major downfall in SERPs.
You may go for free links if you get relevant websites to link to.
A good rule of thumb is to be organic.

Unethical ways do give you faster results but once detected can lead to a major downfall SERP rankings.