Dofollow- If you want any website or page crawl to in search engine.

No Follow- If you want any website or page Not crawl in search engine.

When Google bots are crawling a website they look for external links point to other websites. If this links is “do follow” then search engines will follows the link and so link juice gets passed.

If a search engine finds a “no follow” backlink it will just ignore the link and will not get deeper into crawling and no link juice is passed.

Dofollow links are crawled by search engines and no-follow link are not crawled by search engines.

No follow link would not influence the link target's PageRank and do follow influences...

Dofollow means you are telling Googl to follow the link and nofollow means the opposite. So, to get the best SEO result always opt for dofollow.

Dofollow=Which type of backlink Google are prefered(follow link )first and which type of backlink improve your websites traffic and pr
Nofollow=Which type of backlink Google are not follow and not helps providing your websites PR only improving your websites traffic.