From what we have seen from anime, it clear that cynthia's garchomp is stronger than tobias's darkrai aswell as latios.
Cynthia have also faced and defeated more stronger opponents like elite 4.
So cynthia is arguably more stronger than trainer than tobias.
But these are said only by judging his 2 known Pokemon. Many will say darkrai is his strongest since he uses it more often. But I dont think so.
Cuz there is condition in anime that a trainer's strongest only loses in last moment. This pattern is followed by every single trainer except for ash. Cuz he has pikachu to back him up even though he loses his strongest. (eg : ash vs drake, ash vs flint, ash vs tobias and many more)
In case tobias vs ash, tobias loses his darkrai right from the start (halfway if said correctly).
Instead of losing his cool or worrying about that, he just continues with latios which was just as strong as darkrai.
So it is safe to assume that he has an ace with him.
It can be either his starter Pokemon(a non legendary) or something more powerfull like mewtwo.
According to my prediction his team would be like this :
1. Darkrai
2. Latios
3. Entei
4. Lucario (starter)
5. Zapdos
6. Lugia
( Entei, lucario - shows battling against ash Pokemon in opening song.
Zapdos - from brid trio, which similar to entei from beast trio.
*Lugia - from tower duo, which similar to darkrai from lunar duo and latios from eon duo.
*Most likely tobias is going to have every single legendaries except god tier Pokemon like arceus, creation trio, weather trio.)
Also want to point out the moment when he appreciates gible by saying "your gible could have defeated any Pokemon, but not my darkrai".
Many like to exploit this by saying his rest of the team is weaker than gible.
But this gets contradicted immediately when he releases his 2nd Pokemon latios.
Cuz there no way that poor gible stand a chance against latios.
Btw tobias never said "gible can take out any of 'my' Pokemon".
But lets assume that gible is strong enough to defeat his rest of his team by draco meteor, then his team must consist of dragon Pokemon.
So his team would be like this :
1. Darkrai
2. Latios
3. Latias
4. Dragonite
5. Salamence
6. Garchomp
This team is far less complicated and explainable one. This team also indicates that tobias is a dragon trainer.
Even though its less powerfull than a team full of legendaries, this is also possible.
Many will say he is only strong because he has legendaries. Saying it like he was born with legendary Pokemon. No trainer starts his career with legendaries.
So he has to be insanely strong to catch something like darkrai. And lucario in his team makes perfect sense.
And he is 32 years old, (way more older than cynthia) So this guy is also a well experianced trainer.
Many will like to compare him to brandon since he also uses legendaries. But I will say tobias is way above brandon.
When ash battled against brandon, his torkoal put up a good fight against regis. But this was the same torkoal that got OHKOed by darkrai. This indicates that his power is way beyond any ordinary trainers.
Tobias also has a feat that no trainer in the anime has -
One and only trainer to complete an entire league with just 2 Pokemon.
He is easily the most op trainer ever introduced in the anime.
With all these feats, I still dont know how writers can forget someone like him. I wish he shows up in future.
So finaly....
Cynthia vs tobias
What happened between them is never shown in the anime. Most likely they will never show it.
When cynthia appeared in later episodes, she was still the champion of sinnoh. So it means tobias either lost to cynthia or to elite 4 or he never went up against them.
If someone can defeat tobias then it is obviously cynthia and vice versa too.
Cuz anime never shown a champion vs champion battle.
So the only trainer that has a chance against cynthia (other than champions) is tobias.
And there was one more trainer who was really strong and have fought against steven (former champion of hoenn) - Alain.
But he misses the spot, cause he was strong but not op as tobias. And he lost to seibold(elite 4 member) too.
So the strongest trainers in the anime are (other than champions and elite 4) :
1. Tobias
2. Alain
3. Ash
(Ash recently won the alola league)