UKH

Due to various circumstances I've ended up with 2 pairs of my climbing shoes in my size. Do people think it's better to wear one pair until they wear out or rotate between the two in an attempt to make them last longer?  

Some people like to keep a pair for 'best', where the sole is firm, rigid and with sharp edges. I wouldn't be overly concerned either way though  

I tried rotating shoes but it made my ankles hurt.

Would it make any difference? If my shoes last a year per pair and i have two pairs, I'll get  two year of wear either way.

Although alternating shoes means you'll have to break both pairs in at the same time so it'll be a while before either pair are comfy.

Same situation with me at the moment. Start with pair 1 but  break in the other pair with occasional use. Use pair 1 more until the edge is no good then you'll have a partially broken in pair (pair 2) for when you've sent pair 1 away to be resoled. 

Lots of us have many pairs - a well worn in pair, for longer routes and comfort and a just worn in pair for routes needing a good edge and stiffness.

Rotating them could also make them smell less as they dry properly between sessions. 

If you rotate then you have to buy two replacement at the same time, or have to get them resoled at the same time.

Use one pair, the more-worn pair, for indoors, and use the others for outdoors.  When the indoor pair wear out, demote the outdoor pair to indoors and buy a new outdoor pair.  It's worked for me for 20 years or so.