Depends on what it's chambered in. If you have a .22lr, I'd go with a nice little Nikon 4x or 2-7x Prostaff. Both are set at rimfire range parallax. I have 2 of them so far and LOVE them.
If you picked up a WMR or an HMR, I'd go with a 4-12 or 5-15 in a 40mm AO. I have a Bushnell Legend 5-15x40 AO on my 452 LH .17HMR and it is pretty much perfect. If I had to do it again, I might go with the Legend in 4-12 instead. The Legend line is a fantastic scope for rimfires at a great price point. Bushnell has discontinued the line and is now making the Trophy XLT in it's place but in my opinion, the Legend beats the XLT hands down.