-R allows ANSI colors (and other ANSI features)
-S allows horizontal scrolling (I don't use this one with query-logs though)
-X Leaves the output on the screen after exiting. I mostly use this one out of habit, since I use less as a pager in the CLI mysql program
-M More detailed status message. It'll tell you things like what % of the file is already scrolled.
-N Line numbers. I don't always use this, especially with larger files, but its useful.
-I CASE INSENSITIVE SEARCH!!!