from my experiences (up to 4th gym):
Tsutaja / Jynobi - pretty weak as Tsutaja, when it evolves it's... still pretty weak. doesn't seem very useful so far.
Hiyappu / Hiyakki - Hiyappu obviously trashes the first gym but seems pretty weak until you evolve it with a water stone (in Hiun City, before the 3rd gym), then it becomes pretty powerful.
Nageki - destroys the second gym if you level it up to 17 (gets Vital Throw). has Seismic Toss which works wonders for catching wild pokemon. despite mine being Bold it's damn powerful.
Dangoro - thought it would be shit but it gets Headbutt and Rock Blast and is insanely strong for a little rock thing. probably more useful than Geodude due to the upgrades to Sturdy - if you switch it in on full health it will always get a shot off. slow, and no ground attacks unfortunately, but good.
Miruhoggu - i accidentally didn't learn Crunch which pissed me off, and Minezumi is pretty weak, but Hypnosis is very helpful and this thing is sorta fast.
Haderia - surprisingly good for an early game pokemon. it's a 10x better Mightyena really (and it still has to evolve again). strong and fast and with decent defences.
haven't really used anything else, though i'd say the game is far more suited to training up one pokemon to a really high level over the course of one route then taking on the gym rather than training up a party of 6 evenly. 6 mons aren't going to be much help when you get to the gym and everything is 2-4 levels higher than you...
Tsutaja / Jynobi - pretty weak as Tsutaja, when it evolves it's... still pretty weak. doesn't seem very useful so far.
Hiyappu / Hiyakki - Hiyappu obviously trashes the first gym but seems pretty weak until you evolve it with a water stone (in Hiun City, before the 3rd gym), then it becomes pretty powerful.
Nageki - destroys the second gym if you level it up to 17 (gets Vital Throw). has Seismic Toss which works wonders for catching wild pokemon. despite mine being Bold it's damn powerful.
Dangoro - thought it would be shit but it gets Headbutt and Rock Blast and is insanely strong for a little rock thing. probably more useful than Geodude due to the upgrades to Sturdy - if you switch it in on full health it will always get a shot off. slow, and no ground attacks unfortunately, but good.
Miruhoggu - i accidentally didn't learn Crunch which pissed me off, and Minezumi is pretty weak, but Hypnosis is very helpful and this thing is sorta fast.
Haderia - surprisingly good for an early game pokemon. it's a 10x better Mightyena really (and it still has to evolve again). strong and fast and with decent defences.
haven't really used anything else, though i'd say the game is far more suited to training up one pokemon to a really high level over the course of one route then taking on the gym rather than training up a party of 6 evenly. 6 mons aren't going to be much help when you get to the gym and everything is 2-4 levels higher than you...