In rifle optics I am always hard pressed to go past a Leupold of some description. Just depends on what your needs are to see what will fit, at present I think I have sitting in the safe or on a rifle the following Leupolds...

Rimfire 4x
Vari-X II 2-7
Vari-X II 2-7 compact
Vari-X III 1.5-5
Vari-X III 3.5-10
VXIII 3.5-10
VXIII 2.5-8
Vari-X III 6.5-20
plus a straight 6x and maybe an 8x in the back of the safe.

I also have an ACOG TA01(from 1992) that I am very partial to.

My Kahles ZF69 6x is some really really sharp glass....!!!!!