Ragna is a very well rounded character. Good pressure and mixup, good footsie tools, one of the best defensive options in the game and good damage. Easy to pick up and play. But he'll only go as far as your own fighting game fundamentals will take him. If your fundamentals are weak, don't expect to go anywhere with this character.
Jin is also mostly well rounded. Good footsie tools, good defensive options, an effective zoning tool from his ice projectiles, has one of the most practical overdrives in the game and easy to pick and play. Also worth noting is that he's somewhat of an EX moves character in the sense that he can spend 25 meter to enhance some of his moves. But his overall pressure is weak without meter. His standing overhead doesn't lead into anything even on hit without 50 meter to Rapid Cancel and his other good overhead option TK Hizangeki requires 25 meter. Some Jins try to make up for this by doing resets off freezes.
Taokaka has great movement and great pressure to go along with it. She doesn't have a strong high-low mixup game but she has so many options that a lot of her unsafe stuff becomes safe because you're afraid to push a button and get framed trapped. So often times you don't want to do anything but at the same time because she has moves she can throw in to leave her + on block and ways to stay on top of you, you eventually have to do something and it has to be done at the right time. Truly annoying character to have to deal with once she's in. *is hella salty about this character* Notable weaknesses include low health and poor defensive options. Execution is also demanding from what I've heard.
Valkenhayn actually sounds like he'd be perfect for you. It's a shame that you are having execution issues, though I hear he's demanding in this area as well. His movement is limited outside of wolf form but in wolf form, he probably easily has the best movement options in the game. In wolf form, his walk speed is pretty good so you can do stuff like walk forward, then walk back to bait pokes and punish. His numerous movement options and the speed of them makes getting in on any opponent easy whether they are rushdown or zoning oriented once you've mastered his movement. Once Valkenhayn gets in, true despair begins. His 50/50 mixups are insane in wolf form and he also has a command grab that refills his wolf meter and can be converted into a full combo in the corner.
Prior to the 1.1 patch, Valkenhayn has 2 theoretical weaknesses that are in the end aren't noteworthy weaknesses and then 1 real weakness. His first theoretical weakness is that he can not block in wolf form. The biggest reason this isn't a big deal is because his movement options and their speed more than make up for it in a lot of cases, even dealing with zoning. It mostly only comes into play with wakeup reversals but he has his ways of dealing with those as well. His 2nd theoretical wekaness is that he can only do wolf shenanigans for as long as he's got wolf meter to do so. Unfortunately, even a short combo gotten from a jA starter is enough to give him back enough meter to start his vortex up again as soon as the combo is over. This might change in the 1.1 patch due to his changes. Too early to say. And finally, he has the real weakness that he doesn't have any good defensive options.
Whiffing a chain with Hazama isn't quite as bad as you think because he can still pull himself in, even if the chain whiffs and there are different ways to pull yourself in but his ability to do this is limited. I'm not too well versed on Hazama unfortunately so I can't go into much detail with this one.
Relius is a pretty solid character. He's got good ranged options with Ignis. Though, he really shines in pressure with Ignis backing him up. As Tomo implied, he can force you to block for as long as his Ignis meter will let him. He's got good mixups as well. While Ignis is forcing you to block, he can do stuff like dash forward standing overhead or a low. He can jump forward and either go for jB or do an empty jump 2B. Really good Relius players will do low to the ground air dash jB to make it even more ambiguous which one they're going for. If they see you're getting too comfortable, they can go for an unblockable setup. He's got some decent defensive options with led lay and his reversal gears super. But he can't get much done without Ignis.
That's it. For more info, I'd recommend looking at their Dustloop wiki pages and maybe asking a few questions in the "Picking a Main" thread.