How do you define better? 305/40 is going to be about 31-31.5 inch overall diameter, and just under 5 inches of rubber between the road and the rim. 305/45 will be about 32-33 inches overall diameter and just over 5 inches of rubber between the road and the metal. I don't know what year or what leveling kit you installed, but 33 inches is usually acceptable on OBS trucks, but about the largest you can run without rubbing (and even then they sometimes rub). More rubber means you're less likely to damage the rims in pothose, though I don't know that ~1/2 inch makes a lot of difference.
I personally don't like the low profile look, so I won't comment on style points. As I said, which is better depends on what you mean by "better"
I dont know how high your HD is Lifted but my 06' SIlverado has 9 inches of lift and I have 20's rims and the biggest tire my truck can take is a 35 x 12.5 x 20. Any bigger tire and it will rub the wheel well. HD's may be different but if you have a Off Road truck shop near by they should be able to tell you how big you can go.
For the most part, the more tire the better, especially when protecting your huge rims. The lower profile the tire on your big rims the easier they will dent or crack.
I've taken my truck into nasty places, trudging through mud, sand and rocky trails with no regard for my truck and my rims stayed safe so far.
Also here is a chart with tire sizes and specs that might help.
I have a 2003 silverado ls stock suspension with 22" rims tires size 305 40 r22 and they rub a little when i make sharp turns!! The ride quality is better than if i were to go smaller on tires...
Hope this helps
A forum community dedicated to all General Motors truck owners and enthusiasts. Come join the discussion about performance, lift kits, wheels, tires, modifications, troubleshooting, maintenance, and more!