Miner is vastly superior, at least for the average playthrough in the early/midgame.
Miner turns the average 2 (1-3) ore you get from a node to 3 (2-4), a pretty insane 50% increase. That means you'll on average have to spend far less time/energy/risk less going for ore, will be rewarded far greater on collecting a deposit of ore. A pretty potent combo when you need ore and bars for dozens of recipes in game, most of which are the most crucial machinery in the game for strong progress and advancing through the game.
Something to also note about the label "ore", is that it's also more encompassing than you may think, beyond just the copper/iron/gold/iridium/radioactive ore notes, it also affects the cinder shard nodes, coal nodes, and even the grey rocks in the mines (which are technically "stone ore").
Geologist on the other hand is 50% more gems and geodes from breaking rocks, of which you'll encounter far far less than ore nodes, as well as being far less useful in a general (they of course have specific uses but those don't usually need a bulk amount of gems/geodes and none are needed early/midgame).
Later on, you'll also have to consider your level 10 choice, having two unique options for either of the level 5 choices you picked. Blacksmith (50% higher sell cost on bars) and prospector (coal doubled) both aren't amazing (blacksmith is mostly for those more experienced with the game using something like skull cavern for cash, prospector seems good on the surface but you won't actually see a doubling in coal, it only affects the drop rate from normal rocks which give coal rarely).
Neither are gemologist (30% higher gem prices) or excavator (double chance for geodes) though, at least not in niche situations (like lategame using crystalariums as a money maker or going for geodes for the last museum items).
You'll always have the option to swap back and forth later, but it's almost always in your best interest to go miner for the majority of the game (basically as long as you need mining resources at all).