Not to sound like a broken record, but shit loads of these questions can be answered via chambers & partners in like 10 seconds. Look up the V10-V15ish firms. Pick the market you're interested in. Open litigation rankings. See which are band 1 and which aren't.
You can go further, but it's at least splitting hairs and (more likely) splitting markets and practice areas. Calling Williams & Connolly "better" than the rest of the V10 for litigation is just... weird. W&C does very different stuff, as a firm, than the big guys in NYC (and in some respects, even than the big guys down the street in DC).
And another thing - it always takes two to tango. Every big deal has at least 2 major firms involved and often more. Every big, nasty litigation fight will have lawyers on each side. And as a young lawyer at a firm the little differences just won't matter that much.
If you want to do M&A there are real reasons to look (a) at New York and (b) at the V5/V10ish firms over any others, if the options are at the table - but you just won't have an earth-shatteringly different career if you do M&A at Cravath vs. M&A at Cleary.
As for lit and corp, corp associates do bitch work but also rise in responsibility much more quickly than litigators. A litigator is going to be waiting a lot longer to run a case than a capital markets lawyer will be waiting to run a deal.
W&C is easily better than any NYC firm. There is a reason its the #1 most desired firm for the top students at HLS and YLS. No one on the law review at HYS wants to toil away marking up documents for bankers. All the big NYC firms are basically shops for the big banks. All their litigation is finance focused. That is the reason practicing law in NYC sucks. Who the hell wants to work on banking related matters every day?
Firms like W&C, Covington DC, GDC DC, and Wilmer DC are the most desirable firms for law review forks because of the diversity of different litigation assignments available.