Why isn't there an "either/or" option on the poll? I enjoy either one. But after a time of watching a series in one or the other, I begin to prefer that one, simply because I'm familiar with the voice actor and they've become synonymous with the image of that character in my head. Switching after becoming used to one is like all of the actors in your favorite live-action TV show suddenly being switched out for all new ones. Adjusting to that is just something the mind resists as much as it can.
Most of the reason I'm halfway is because, typically, I have little input in which language I'm exposed to. I'm in an anime club, so there it's really up to the person who brought in the series. All the others I watch I've picked up from Funimation's submissions online, and usually on those they offer only one or the other (or, if they do offer both, the episodes in subs are usually much farther ahead than the dubbed ones).
The only ones I've really had much of a say in is the Hayao Miyazaki films I own. Just by habit (and because of the DVD defaults) I've always listened to them in English first.