what is better for SEO: 3 backlinks from one and the same domain with high pr.. for example domain1.com pr5 or 1 link from high pr5 (domain1.com) 1 link from pr2 (domain2.com) 1 link from pr2 (domain3.com)
It depends upon the type of links, the actual quality of the site (PR means nothing, easy to manipulate or fake) in terms of authority, trust, stability (a good link profile of its own). Better off checking the site (or sites) with Open Site Explorer. This isn't completely foolproof, but if you're not sure about a domain's authority it will give you an idea.
Edu links spread out along your sites and deep page backlinking I offer this kind of service works well for my sites
For me both has its own important in terms of passing link juice. It solely depends upon the type of links and the actual quality of the site in terms of authority, trust, stability. You should check the quality of websites before getting links from them. You should also check link profile and should confirm whether they are spammy or not. Hope this answers your question..!!!
I'm just asking should I focus on getting links from 5-10 websites with very high authority or it is better to post links on 50-100 websites with lower rankings but still in my niche. I'm not talking about spamming in any way. Just curious what is better for google and getting traffic.
You can go with getting links from 5-10 websites with very high authority websites in your niche. This will help you in better way and will enhance your link profile too.
I guess it is better to have many backlinks from high authority sites and only 2-3 backlinks from minor sites.. anyway small sites update their content slower and links would be on top a longer period of time.
You're really not getting the point. It's quality, not quantity. You seem to be talking about blog posts when mention "on top a longer period of time". If you're talking guest (not paid) blogging then you'd be better off with one guest post on an authority site. Wider audience, not just "link juice". Think beyond search engines and consider audience, gaining visitors.