On the BH side, I would recommend the 'parasite' approach as the new Web 2.0 (if you pick the properties that Google doesn't penalize, they work better than traditional Blogger et al subdomains). As for WH, using both social media and forums are also recommended, especially if you concentrate on the ones with higher traffic.
In general, it's preferable to select urls to place your backlinks that already have real visitor traffic to build rank, for example from guest posts (to save money, stick with free guest post sites that have Alexa ranks under 200,000, as that will screen out the PBN sham guest post urls).
Another source for good ranking in 2019 are 'aged' contextual links on sites that have real traffic---if you can get a webmaster to update an existing page (that has high metrics) to put your link on it for a one time fee (say $100 or so), that's arguably better than buying an expired domain for PBN purposes and maintaining it for $100 or more per year (registrar fee and hosting).
