One of our favorite datamancers, Balco, with whom you're hopefully well acquainted -- and if you're not, here's an in-depth interview we did with him a couple of weeks ago (link) -- recently calculated the difference in win rate for the most common Champion combinations, depending if they attack first (in red) or second (in blue).
Main takeaways if you're not playing with/against lurkers:
- Most differences are small enough to fall into the "don't sweat it" range,
- Some decks (notably Thralls, but also Darkness and Legacy Poros) actually prefer going second,
- Riot certainly did a great job in making the coin a small factor (see "don't sweat it" above).
Main takeaway when Pyke and Rek'sai are around: Lurkers is indeed a highroll-y deck. Depending how the coin goes, Pyke & pals are either the worst Meta deck (and by a long shot at that), or one of the best (nearly matching Ahri Kennen).
For reference, here is Balco's original tweet.
And somebody, please, get that man a Ko-fi! =)