What are the technology and design parameters that mostly affect yield?
The total die size has a big impact in yield.  Bigger dies mean less total dies from a single wafer, which means you might have 1 bad die out of 50 dies for a big die, instead of 1 bad die out of 100 dies for a smaller die.  An imperfection on a big die will kill that whole wafer area, where you could have fit 5 or 10 smaller dies, and only 1 die dies as a result of imperfections.

The edges of a wafer are typically where the most imperfections occur.  With smaller dies, you get more dies away from the edge of the wafer.  Bigger dies result in more dies sitting closer to the edge than that sweet, juicy silicon in the center.

Feature size also plays a role in yield, especially when first rolling out a new feature size.  AMD and nVidia both got hurt by TSMC when they went to TSMC's 40nm process back in 2010 for the Radeon 5000 and GF100s, respectively.  Initial yields were down in the 40% range.  But here in 2016, nVidia is using TSCM's 28nm process with good results.  My google-fu hasn't been able to get hard numbers on the yield.

Small feature means advances in lithography, and that means problems, as with everything on the bleeding edge.  Using TSMC's 40nm process in 2016 should give high yields because it's now a mature process.

In short, if you're looking for absolutely highest yields, small dies with big feature sizes will give the biggest yields.