Optical Sight for my Ruger .22 Autoloader?

[dovehunter]

I have been considering for some time now installing some sort of optical sight on my Ruger .22 autoloader. My shooting would be plinking, (very) informal target shooting, and definitely some squirrel hunting too. At my shooting club's range I've tried others' guns with both (what I refer to as) red dot sights and low power scopes. I like both but can't decide which way to go. What do you guys use and/or prefer and what are the pros and cons?

Also my gun is one of the older models - there is no "MK" anything written on it and the receiver is not drilled and tapped. Are there any reasonably priced mounting systems out there other than the B-Square Universal that I could use without having to remove the rear sight and/or drill and tap or otherwise alter the receiver?