It doesn't really matter. Either way, your new pass will be backdated to one year from the expiration from the original pass.
You have a one month grace period after your pass expires to renew in person. I usually renew in person simply because I don't want ot have to keep track of a voucher. When we drive down, I usually stop at the Ocala welcome center and renew it there. No particular reason, it just feels like we start our "vacation" a few hours earlier that way.