This is my personal view on optics-
For a plains game type rifle: Rule of thumb is 2x magnification for each 100 meters you wish to shoot. So, a 30-06 or similar, which is generally a 500 meter rifle (at most) would get an optic that goes up to 10x. For myself, my vision isn't perfect as I have aged. I tend to say 3x per 100 meters. My plains game type rifles wear variable power optics ranging from about 2x-12x or so. I have a few that go to 14x and I like them, especially for range work as I can truly dial in the zero. Never assume your zero at maximum magnification is the same as it is at lowest magnification...always test it.
Objective size is relative to your shooting style, rifle, and body type. For a 2-12 variable power optic, I generally want an objective lens around 40mm or so. Big objective lenses cause you to mount the optic higher...which then means you stock shape might not be able to get your head/eye up to alignment with the optic and you need to be looking through the center of the optic. Larger objective lenses really aren't that much of an advantage, assuming you are using a quality optic.
Eyebox is an issue. A forgiving eyebox on the back end will give you a lot of wiggle room to compensate for field positional shooting. Shadowing will show you how forgiving your eyebox is.
Eye relief...I like around 3 inches or so.
Tube: 30mm is fine. Really, 1 inch is fine too. More tube gives you more adjustment for your turrets but you rarely need it unless your mounts/rifle are somehow not square.
Reticles are relative to what you want it to do. Most hunting optics are 2nd focal plane, so the reticle is not going to stay consistent in terms of size, relative to to target, as you increase magnification. This is generally fine for hunting use but if you want to use a specialty reticle that calibrates range/adjustment...2nd plane makes that hard. 1st plane optics are more expensive, heavier, and the reticle will remain consistent, relative to the target, regardless of power. This actually can be annoying at some settings as the reticle looks huge. However, if you wish to use a "Christmas Tree" type reticle with built-in holdovers, you should go 1st plane.
Illumination is great but keep in mind, anything electronic will fail. Batteries leak and die. Never store them with the battery in. I like basic illum...but I am fully aware that it can fail and cripple an optic. Test waterproofing on it in your sink.
Brands- I prefer Schmidt and Bender. I've used them for a decade during some hard use situations and they flat out work. They are heavy, bulky, and durable. Swarovski and Zeiss are also great. I have 2 Leica riflescopes and both have some minor optical flaws that make me leery of buying more. They were early models though.
Mounts are just as important as the rifle. Brownells sells scope alignment tools. Always assume your rings are not true/round/aligned. I bought the lapping tool and it works well. Use a proper torque wrench and don't overtighten. You will damage the scope. Loctite all things screw related. Blue only.
For dangerous game...all of the above applies but it needs to go to true 1x and a red dot illumination is ideal. Removable optics are nice for DG rifles.