i wanna buy one...which one u guys think for 3s? ty!

Darius can 1 vs 2 in 3 vs 3...

Any character can win a 1v1, 1v2, 1v3. It depends on how smart/coordinated/built/positioned the enemy are.
Riven I absolutely LOVE for late game(her early/mid game are also very well too). Her ultimate is such a massive damage increase plus a ranged execution with extra range for abilities/auto-attacks. Damage Riven with a guardian angel is just lovely.
Darius is different. His early game/mid game are his key points. He can bully people out of lane and execute them properly at 6. His passive is like GangPlanks but gives him a better advantage when he uses his ultimate. Late game Darius, in my opinion, is just sit there and take damage while executing the enemy if they are low. Tanky Darius is recommended(from me).

In my standpoint, I adore Riven. So I would buy her(even though I own here, but for your sake)

im having the same problem as craniux, which one should i get? im a good solo top brusier, which one fits me more? i also like jungling. the reason why im having trouble choosing is because riven has the broken wing abillity and seeing people play with riven and use that abillity looks like a lot of fun, she also seems really strong late a mid game. i really like darius because you can prevent ur teamates from kill stealing from u or kill steal your self with your ulti, his combo also seem really cool. Which one is better for me?

Riven is actually worth buying and is actually fun to play. Darius has the most boring kit in the game. He is annoying for all players in the game except himself.

ty for responses i bought riven...and its true she is a lot of fun, but darius is a pain in the *** to lane against.

Darius is the more overpowering champion, his decimate is lethal. On TT he can 2v1 with no problems and will usually be getting the triple kills late game. 5v5, a combo of J4 and Darius can 2v5 (Done it before ^^). Back to TT, it might just be me being decent at J4, but i can dominate a riven early and they really aren't a problem. A Darius with some knowledge of how to play him is a major problem to any top champion. I'd say Darius > Riven, because Darius doesnt have to be fed to be effective.

Do you want to buy a character who is:
A.) Fun to play with a versatile kit and enjoyable mechanics
B.) An extremely boring and repetitive champion who kills the game's fun for every party involved.

If you picked B - congrats. You are now the proud owner of a brand new Darius!