How important is it to choose the right editor on journals that require you choose an editor?
The editor is the person responsible for directing your paper to a competent reviewer. Taking that into account, I'd strongly suggest you choose the editor that is most related to your research area, because he will have more contacts of experts in that field. Your advisor's knowledge on some editors can probably help you discover which ones hold this position, but you really should have this information on all of them. E-mail the journal and ask for this information before you do the legwork.