My preference is for the Leupold scopes. They have a number of models in their "RIMFIRE" line. These have the parallax set for 50-60yrds. This is VERY IMPORTANT!
If the Leupolds are too rich for your blood, that Nikon 4X is a good scope and is a bit cheaper. I recently picked up a used Monarch 4.5X16. I was happy with the clarity and resolution of its optics.
OR just buy the best you can afford, but get an ADJUSTABLE OBJECTIVE!! Simmons, Bushnell both have satisfactory offerings.
Don't be too hung up on setting it for every shot, set it close to what you figure the shot will be (OR 50 YRDS) and this will suffice.
Good luck,
CW