I've been known to wait and make my tweaks during sound check with the band, using the following method...
If I find that I need to EQ too many of the input channels in the same way, (for example, cutting the upper-mid on almost every channel,) then I see that as a red flag that the system needs tuned to compensate. I'll make the same adjustment to the L/R EQ or system DSP until the majority of my input channels can return to normal, (i.e., sound good without much EQing). Of course, there will always be those few channels that do need harder EQ, but you get the idea.
That said, since I've gotten my new mixer and new speakers in service, I haven't had to touch my Main L/R EQ much at all. The system sounds pretty damn good in almost every room I've had it in so far.
Even so, I still like to put in a test song or two just for reassurance that things are sounding good. I prefer songs that are clean and well recorded, and which include a variety of different instruments.
My goto songs are...
Dry Cell - Last Time (The reprise version that starts with piano)
Poets of the Fall - Stay
And if you want to hear your subs, these two songs have low rich bass...
Chevelle - Comfortable Liar
Sammy Kershaw - Cotton County Queen
I've heard them all enough times on enough systems that I know how they should sound.
