Web2.0s would be good , get going with nofollow backlinks at start , as ******** would directly get harmed !
what ?!? How can d-0fol-low links hurt you? You have no idea what you're talking about, mate!
OP: web 2.0s are pretty useless nowadays. If you get 100s of them you might be able to move some long tail keywords a few spots in the SERPs, but even that is not guaranteed as google has devalued most links that are free and easy to get like web 2.0s
If you want to get links that matter get quality PBNs, quality guest posts, or quality niche edits. Any of these 3 will work if you have a good SEO strategy in place. And speaking of strategies, you said that you have no idea how to rank your sites, and in this case backlinks are your last worry.
You need to start with analyzing the competition you'll be up against first, because if you go into a ultra tough, ultra regulated niche (like medical, web hosting, finances, banking, travel, loans, insurance, lawyers, SEO, etc...) you'll be eaten alive by the big dogs (SEOs with millions of $$$ monthly budget for SEO), not to mention that it takes time to rank in these niches (1-2 years at least), and you'll need a strong brand / domain, and strong brands / domains can only be built with big budgets in these niches...
So, first of all pick a niche that you're comfortable creating content in (because you're gonna need a lot of content), then analyze the competition in that niche (so you're not against big brands, or other affiliates... although, if I'm being honest most niches are taken up by big brands and affiliates nowadays), and - more importantly - spend some time on keyword research because finding keywords that you can rank for within a few months (and preferably without links) is your best approach to SEO as a newbie.
After you find some good keywords in an approachable niche, focus on creating quality content. In this time and age, quality content and good site structure can beat strong domains with 1000s of ranking pages and high DR, but you need to get your keyword research and content creation right.
And if you do these things right and you're still not ranking anywhere... or anywhere meaningful I should say, then and only then it's time for backlinks. Just don't go for web 2.0s right from the start as they won't do anything good. Web 2.0s are useful after you build yourself a presence in google and you need to diversify your backlinking profile (which is pretty important to do) so that you won't look like a link builder to google because sites that acquire links organically are supposed to acquire links from lots of sources, not just from web 2.0s.