The simple rule of thumb is : the lowest magnification at which you can achieve the desired accuracy, at whatever distance used....is the best.
Magnification magnifies "the shakes", which we all have. The higher the magnification, the harder it is to hold steady on target and the more small movements become disruptive to good accuracy.
Obviously, the more stable the platform from which one is shooting, the better. Higher magnification is far more usable, if the rifle is fired from a stable rest. Off hand, or from an improvised rest, higher than minimal magnification is often counterproductive.
So, if you can achieve "benchrest" competition accuracy at 1000 yards with 2X, then that is what you should use. Obviously, few of us (or none) could ever do that. By the same logic, shooting off hand at 100 yards, using 12X is probably not going to work at all.
Everyone has got to figure out what works for himself/ herself, in this regard. The rule I use for myself is just enough magnification to produce a 50 yard APPARENT viewing distance. In other words, for 50 yards.... 1X. For 100 yards....2X. 200 yards.....4X. 300 yards.....6X, etc. etc. Of course, compromises must be made, based on the magnification range available.
So, if I were to suggest a single scope type for 0 to 300 yard shooting, with the flexibility to use the same scope for hunting as well as target shooting.... I'd go with something like 2 - 7X, or perhaps 3 - 9X. Frankly, 18X, even at 300 yards, is a bit counterproductive, in my opinion. Others may disagree - and that is fine.
As for zero point changing with changing magnification, that is a function of TWO issues. One, the QUALITY of the optic. Two, the overall magnification range of the optic. It is very difficult to engineer a scope that has a magnification range of 4.5 - 24X to NOT have enough optical error built in so that zero won't change with magnification change. This issue is less difficult with a range of 2 - 7X, however. The result is that high-powered scopes, if of any real quality, will be expensive. So, if you decide on a high magnification scope with a really wide magnification range, you'd better plan on spending A LOT. Adjustable objectives are useful for long range shooting, not so much for only a couple of hundred yards. AO allows parallax to be adjusted. Most non- AO scopes have parallax set for 100 yards, which is good enough for shooting from 0 - 300 yards.
Anyway, the choice is yours. Whatever you choose, I do recommend buying the best quality optic you can, which is not necessarily the most expensive. But, if you spend only $100, as regards optics, you'll only get junk. Don't scrimp on scope bases and rings, either.