You're going about this the wrong way. Depending on the magnification a scope with a 20mm objective could let in more light and be brighter in low light conditions than a 50mm objective. The more magnification you have, the bigger front objective you need. A variable power scope set on 8X with a 40mm tube lets in all the light you can use. Which is exactly the same as a 4X scope with a 20mm tube or a 10X scope with a 50mm objective. If you don't need more than 8X then you don't need an objective bigger than 40mm. If you want more than 10X even a 50mm objective isn't big enough.
And the quality of the glass trumps objective size within reasonable limits. A 10X optic with a 25mm objective like you see on many binoculars will be poor in low light regardless of the lens quality. But high quality 8X glass with a 32mm objective may well be better than lower quality 8X glass with a 40mm objective.
A 30mm tubes only advantage is more adjustment range for shooting at really long range. But they are sorta growing on me too and I like them even though my practical side tells me they aren't necessary on a hunting rifle. They are a little heavier.
You can't really go wrong with a 3.5-10X40 Leupold VX3i for the money. As long as you don't go over 8X in poor light they would be a good choice.
This is my favorite hunting scope. Meopta used to make this scope and place Ziess badging on it. It is the exact same scope as the now discontinued Ziess Conquest 3-9X40. They made them for Cabelas for a few years too with Cabelas name on them.
https://www.swfa.com/meopta-3-9x40-meopro-rifle-scope-6.html?___SID=U
I don't have this exact scope, but do have a fixed 6X just like it that I REALLY like. This checks off all of your boxes, 30mm tube. 3-9X magnification and 42 mm objective. If it is as good as my 6X fixed power then it is a great scope.
https://www.swfa.com/swfa-ss-hd-3-9x42-tactical-30mm-riflescope.html?___SID=U