I'd go with the scope Cole suggested. Wish I could find there new crossbow scope to put on my Dagger.... Alternately maybe a Nikon Prostaff or Monarch or maybe Leupold.... Don't let Vortex find out you bought something else! :p
I would go with a 4x12x40. Brand really depends on what you want to spend. I bought a nice Burris for my son's 06 that was pretty reasonably priced. Sent from my SAMSUNG-SGH-I317 using Tapatalk
I've always loved Leupold. I have a 2.5-8 VX-3 that I've used and abused for years without issue. Not sure if you want to spend that much on his first scope though. I bought my first scope when I was 14. It was a 3-9 Bushnell that I picked up at Fleet Farm for about $100. It served it's purpose.