Greenhill Chicago vs WB Chicago

Greenhill provides advantages over Blair from a PE recruiting standpoint, but more so because headhunters probably rank GHL higher on the prestige totem pole (bigger deals, bigger dicks type of mentality) rather than because of any material differences in experience / skillset obtained.

I also agree that you see many more "diverse / interesting mandates" at Greenhill (e.g., take-privates of public companies, divestitures, take-over defense, strategic alternatives, restructuring, etc.) However, the overwhelming majority of the PE landscape (LMM to UMM - but honestly true even at megafunds) is focused precisely on plain vanilla M&A. Your "interesting mandates" - while maybe valuable from a holistic career perspective - probably don't matter much too much for someone gunning for a PE associate spot 6 months into their IB stint.

Re: technical capabilities, any bank / group that generates respectable deal flow (yes, even MM deal flow) and actually executes M&A would provide adequate training. Analysts in such groups will get reps building bottoms-up projection models - as well as performing a slew of other analyses like customer/financial retention, TAM, whitespace, SKU analyses, waterfalls, etc. This the type of experience (in addition to general investment acumen and understanding how buyers approach the diligence process), that PE firms care about. It is really only through a "vanilla sell-side M&A" process that you have intense, prolonged exposure to such things.

By the way, any semi-retarded monkey should be able to self-study "merger-math" / 3-statement modelling / acc-dil dynamics over the course of several weekends. But these are more bells-and-whistles rather than the core demands of PE I mentioned previously.

Summary for OP: pick GHL over WB (especially because you explictly expressed interest in Megafunds and WB does not work on mega deals). But if you end up at GHL, I would value and focus more on the "vanilla M&A sell-side" experiences than everything else.