Who would use only one site type for tier one these days? "Hello - I'm a self promoter..look how every direct link to my site is WEB20... please ban my ass"
All that's needed for a great first tier are sites that allow content, have a static URL (for subsequent tiered links)and have decent Page rank (and mostly - but definitely NOT exclusivley d0follow)
Not that D0follow matters much (if at all) for anything other than accumulation and distribution of Page rank. It has precious little to do with SERP's in the past 8 months
19th July 2012 - the day of the 2nd un-natural links warning (the one that was followed by the semi retraction almost immediately)
That was the day they turned on the "Are you gaming Page rank" aspect of their over op snooper
Then turned it down a lot. It was a funny day all in all. Big business sites who interlink and have been around for years were built before "rel = n0follow" was even invented, and they were being demoted. Donald Trump's old money advice site, Bloomberg (Bloomberg FFS) and other sites temporarily slipped way down for their key search terms...these were the BIG boys - and they slipped PRECISELY BECAUSE TOO MANY OF THEIR INBOUNDS WERE D0follow.
Too many d0follow - not natural...
The follow attribute was designed just to be a tool to calculate and distribute PR and nothing to do with SERPs. Since overop, sites with an un-natural amount of d0follow links have been hit as hard as most - and the number of links with d0follow that would natural is decreasing all the time as more and more sites turn on the "n0follow" attribute.
Not denying that exlusive follow links used to be great - the best - as recently as 8 months ago.
So did just using 1 keyword exclusively for anchor text,
So did hammering the same platform type for all your links
So did posting the exact same content on every site
Not natural. All had an affect on many guys ranking (though not as much as some scaremongers make out). = d0follow is exactly the same - and we are talking about an attribute that was never designed to directly affect SERPs in the first place!
This talk about "WEB20" as a first tier exclusive and "D0follow links" exlusive is so 2012..early 2012 at that
Variation and natural linking is the key. Having a first tier that is exclusive ANYTHING all the same link type, same anchor text, same platform, same attributes, same surrounding content... it's all a red flag to Google. 60-40 D0follow is what I use now, and iot works a charm, but I'm aware that as more and more sites turn on the "rel - n0follow" attribute, I might have to adjust that downwards to stay natural.
Scritty