The Most Underrated Professions in Stardew Valley
Agriculturist: All crops grow 10% faster.
Agriculturist is often overlooked because of Artisan but the description makes it misunderstood -- 10% is always rounded up, so planting crops with a 4 day harvest time means they are harvestable in 3 days instead. The essentially reads as "All crops gain the benefit of Speed-Gro (and stacks with any fertilizers, including Speed-Gro)." It makes end of season planting for poor planners slightly more efficient since you can start crops a little later and allows the Farmer to plant Wild Seeds in the winter much more effective (more harvests means more seeds, which means more harvests). Even for vine crops, like Cranberries, this profession is useful -- specifically for Cranberries, you can till and plant Cranberries on the first day of Fall without watering the seeds and still five harvests and you can plant/water Cranberries on the second day of Fall with five full harvests (it's nearly impossible to till, plant, and water all of the Farm in a single day regardless of player level and/or energy).
The only real drawback to the Agriculturist profession is that you'll spend more time harvesting crops than doing other aspects of the game, like fishing, foraging, or mining.
I wish this functioned slightly different -- making all crops grow 1 day faster, so it interacted with Speed-Gro in a simpler way... but all you really need to know is that Agriculturist + Deluxe Speed-Gro reduces the harvest time of those 4 day crops down to every other day and that effectively doubles the value of those crops.
Miner: +1 ore in every vein
Ore is such an important commodity throughout the entire game that you can never have enough.
The Miner profession seems to also affect the unique Stone nodes that produce stone; without this profession, these nodes typically produce 1-2 stone but with this profession you'll get 2-4.
Forester: You'll obtain 25% more wood when chopping trees, stumps, or logs
In all of the time I've spent playing Stardew Valley (over 850 hours at this point), I've never felt like I've had excess Wood. Between Tappers, Crab Pots, Bee Houses, and buildings, I find myself having to buy Wood from Robin and the cost adds up after a while. In one of my most recent Perfection runs, I went Forester over Gatherer and the 25% increase makes a huge difference. Very early in the game, I was able to sell Wood to Robin for tool upgrades or seeds and I was able to mass produce the equipment I seem to enjoy the most in the game.
Mariner: Crab Pots won't produce junk items
An overlooked strategy in Stardew Valley is using Crab Pots to mass produce Sashimi for 75g per Crab Pot. Some of the most profitable crops in the game net ~50g/day per crop tile and consumed a lot of time and energy for the Farmer (especially in the first year, before you have access to Quality or Iridium Sprinklers). Even after you factor in the Bait costs from Willy (5g/bait), each Crab Pot will net 70g/day and won't consume any energy. Up until the Mariner perk, trash makes this strategy less profitable but the trash can be recycled into Coal, Cloth, and Refined Quartz in the meantime.
There isn't an underrated Combat profession in this game. Just take Fighter into Brute and don't worry about anything else. One could make a case for Acrobat here if the hammer special attack is exploited but the enchantments added in Patch 1.5 make that profession mostly obsolete.