Stay with the same brand. Take the key with you when you buy the new door knob, and they can change the lock to match the key.

I've bought 4 homes and each of them has had a different key for the front and back doors. I wouldn't even bother rekeying the new lock.

The existing key cylinder can probably be put into the new lock set if you stay with the same brand.

Home Depot and Lowes will rekey for a very small charge if you buy from them.

A locksmith will re-key an actual lock cylinder, new or old, to any compatible existing or new key. I love having matching locks, but whether it's worth doing to a house you're selling is, indeed a questionable proposition though unless you'd prefer it that way.

I had my locks in my house re-keyed the same, but different if you know what I mean, you don't know how many old keys to your house are out there.