Not that you asked for advice, but I'd actually take the one that's been around longer. New mags, you just don't know if they'll even make it to #1, much less #10. If this was me, I'd probably shoot GroundUp an email like "Sorry to be a pain but I haven't heard from you in like three months and I'm getting a little stressed. I'm excited to be in your mag, and I'd love to have a general publication date for my piece." (probably not those exact words lol)