Adamantite Waraxe

The axe and the chainsaw at each Hardmode tier chop at the same rate. The difference is how they feel in the hand. A chainsaw runs continuously while you hold the button and stays parked on a trunk, so clearing a forest is less tiring. The waraxe is a normal swing you can also point at something that bites, which suits mixed underground work where you are chopping and fighting in the same trip.

Rerolling this for mining speed is mostly wasted money. Rounding puts several cheap prefixes level with the best one, so anything that improves speed at all gets you the same result. Only chase the top roll if you genuinely intend to swing it at enemies.