Tier 1---About 2 dozen manually created "all star" links, all contextual, keyword in title/url, high actual PR/PA, varied link sources (authority news site, expired domain, niche-related guest post, premium Web 2.0, etc.).
Tier 2---About 9-10+ good contextual links to each tier 1 link, moderate PR/PA, some automation okay.
Tier 3---Hundreds/thousands of links to the tier 2 links, can be mainly SB, GSA, NHS, etc generated, smart blasting and so on.
This should lead to a natural looking link profile with natural link density and diversity, for longer term high rankings.