To answer OP's question, Irelia is a very safe, reliable pick in all stages of the game. Probably one of the best all around top laners. Standard build is Tri Force into tank, with a potential 2'nd damage item thrown in at some point (BotRK, Ghostblade, & Zephyr are all common & popular items).
Darius is one of the best top laners to play into bruisers, as his damage is really friggin high naturally, but can get kited really hard by ranged champs, and gets shut down in team fights by CC. That said, if you can outplay and hook an enemy carry with low mobility, Darius has good sticking power with W, and high enough burst damage to kill squishies outright with his full combo. In teamfights, I generally prefer playing Darius as a peeler at first, shredding down the front line, and getting resets on my ult so I have the option of diving into the enemy backline if necessary. If you're getting shut down in teamfights, you can play Darius as a split pusher, although his low mobility means that a clean get away isn't always possible, nor is getting a kill 1v2 (or more), so you'd better hope your team is good of taking advantage of the map pressure you're providing in those moments where they send more than 1 for you. My preferred build is Phage or Cutlass into some tank items (if I'm going to teamfight), or into Tiamat if I'm going to split push. I often will take Flash + Ghost for team fighting, or Flash + Exhaust/ Ignite if I really want to duel.
Riven's laning isn't as good as either of the aforementioned, but if you can pick up some kills or farm really well, she's a beast with items, and has the highest stomping potential of all three. Her AD scaling is the strongest and most natural, and if you really wanted to you could go for a tankier bruiser build that will still do damage, but have better survivability. My preferred Riven build:

Very high damage, but also decently tanky, and you have a ton of mobility. If you want to go full damage, you could forego Randuin's and SV for a GA, and get a 5th damage item like Bloodthirster/ Infinity Edge. If you wanted to go tankier, you could drop the Brutalizer item and go for a GA/ Warmogs/ Banshee's/ Thornmail, depending on your needs.