Consistently when I am on Champion select, the client lags when it is time to select, making it so that I cannot select my champion in time, so it forces me to dodge. Even after I have selected a champion and am waiting for others to select, the lag while others are selecting champions slows my computer.
I think it's mostly an optimization issue, rather than an issue with the network.
This board is the best place to discuss the client with Rioters and your fellow players, although it won't be our main source for feedback resolution. Look to the other tools, like the Submit Feedback button in the client, for that. As always, please follow the Universal Rules and keep content focused on appropriate topics for this board.