I will compare by forms
Kuuga Mighty = most basic character in game, all 3 of his moves are rider kicks, his combos serve to knock opponent away and charge Rider Gauge
Den-O Sword = DenGasher Slashes for up close combat, Extreme Slash (chargeable to break Guard Gauge) exclusively for mid-range, and aerial DenGasher Toss for runaway. Break opponent’s guard then rush with combos and DenGasher slashes, basically. He is better than Kuuga Mighty
For secondary forms, I first note that Gouram assist sucks compared to DenLiner assist, DenLiner covers good area and deals big damage, while Gouram will miss alot and deals lesser damage. Both are unblockable, and both can be avoided though.
Kuuga Dragon is bad in my opinion, he could be Agito Trinity level bad, but his speed is better. Kuuga Dragon = close-range char oriented purely on combos, most of which knock opponent away from him and cannot be followed. Plus his Upward Staff Poke special move is a single-hit low-damage attack that knocks opponent away and cannott be followed, plus its blockable and deals low amount of Guard Gauge damage. I fail to see its use, it looks like a candidate for worst special move in game.
Den-O Rod Form is pretty good, safe character.
-He has projectiles to spam from long range
-his DenRider kick is safe as triggers only if his long-range rod toss connected to opponent
-his fishing attack drags opponent closer and paralyses him (“Get Over Here!!”, anyone?)
-he is one of few characters able to do “turnaround” attack that opens opponent’s back to you
-his combos are very good
Kuuga Pegasus is very solid, one of best marksman characters in game. He has
-forward shots
-anti-air shots
-backdash shots
-guard gauge-breaking shots
-can do shot combos from melee attacks
-He can fly on Gouram around arena, being hardly touchable (his movements works as evades + he is high enough and no one aside of him has anti-air shot) and shoot from there; and guess what, it blocks assists of opponent since Dimensional Portal stays open and opponent cant open own one to summon assists.
Den-O Gun Form is all about flashy stuff, but in truth he is a flawed character
-he has long shot combos that start from shots and dont track. You roll from them, then go and beat him
-his Wild Shot has long startup and is blockable. It tracks but you still can evade it with constant rolls once you spot its startup
-Breakdance Shot makes him completely vurnerable between end of breakdance and two final (standing) shots
-Jump Spinshots miss ALOT
Kuuga Pegasus beats him in everything aside of assist, but then again Kuuga Pegasus can just fly on Gouram and Den-O will stay without ability to call DenLiner
Kuuga Titan is top tier material
-he is unstoppable with his superarmor
-deals big damage
-Gouram can pick up opponent who just got hit with Calamity Titan (Kuuga Titan himself cannot follow that attack with others)
-can combo from Falling Sword Stab
-can combo off own Throw (which is unblockable).
-Off Throw, he can pull 59% combo without roman cancels and 80% combo with 1 roman cancel
-he also has a loop if you use many roman cancels, but its breakable since its based on throw combos and opponent can just use Throw Escape on second throw and break free
Den-O Ax Form is good too, but not as good as Kuuga Titan
-he is too unstoppable with superarmor
-Dynamic Chops are unblockable, can start combos + will hit laying down opponents
-problem 1 is that Dynamic Chops are hella slow and opponent can escape
-problem 2 is that laying down opponent can Ground Recovery so hitting him on ground isnt guaranteed
-problem 3 is his combo potential, his combos are very limited and take around 50% max
So
Kuuga Mighty < Den-O Sword
Kuuga Dragon < Den-O Rod
Kuuga Pegasus > Den-O Gun
Kuuga Titan > Den-O Ax
Other thoughts
In Tier List, I think two lowest positions would be
…
Kuuga Mighty - Kuuga Dragon
Agito Ground - Agito Trinity (bottom tier)
Dunno how this affects tiers, but DiEnd completely owns Ryuki Survive, simply because Ouja keeps Dimension Portal open for loooong time and Ryuki Survive stays without all of his special moves excluding the non-damaging Tractor Beam
BUT if opponent isnt DiEnd, then he suffers because all special moves (everything with X and O buttons) of Ryuki Survive are unblockable. Probably the ones less affected would be Titan / Ax (superarmor) and Kabuto / Faiz (evasion via superspeed modes)