For me it's OLS hands down due to LSCache, it's allows for Caching, Image optimisation, Database Cleanup and more... Basically 3+ other plugins rolled into one, and I've had no issues with it on big or small websites and on OLS or LSWS for the past 6 years.
NginX is great though and have nothing bad to say about it, minus the missing .htaccess compatibility.
LSWS > OLS > NginX > Apache
At least for me. That said depends on how many sites your hosting, if you're a hoster then OLS will likely become a bottleneck without significant tweaking over LSWS.