These two have been my best champions this season, but they've brought me a great amount of pain in terms of learning. Jayce is incredible difficult as a champion and my team usually doesn't understand how they should play around him late game, which has frustrated me to no end. The tank meta in the jungle/top lane and the fact that he created lopsided team comps also brought me distress. Rumble is a comfort pick and one of my favorite champions in the game and I hope to practice him more in team based settings as I've had some really tough games in solo queue.
If I main Riven, what champion compliments her in covering all top lane match ups and who should I pick when the opponent takes Riven? Like I mentioned in a previous post, practicing my mechanical ability and understanding of cooldowns/skirmishes really attracts me to the champion. I'd guess I would settle on Lulu (and perhaps Ori) for mid/top/support and Nidalee or Ekko for jungle for when I don't get toplane.
Jayce is pretty damn great and he's also one of the champs that can easily deal with Riven. A self peel and poke? OP match up for Riven. He's also great since he can be a flex pick top/mid/adc. He thrives in the poke meta and pretty much deal insane damage once he picks up muramana and a last whisper. An underrated champ if I say so myself especially now that the meta is shifting from tanky top and jungle to a more carry oriented ones. Rumble on the other hand is just a great team fighter. He can turn team fights around so well. He's a tanky ap bruiser who deals tons of damage in pretty unsuspecting ways due to how his kit works. It's pretty hard to manage his heat levels and it's the difference between great and average rumble users.
If you want to use Riven effectively then you need to have someone on your team be a primary engager. Riven is really bad at engaging team fights because she has to walk in close to the enemy before dealing damage seeing that she's a melee. You can't use your skills to close in cause that would mean you would lose your damage output. We usually remedy this by having flash to engage. That's why distortion boots is great on Riven. Now if you don't have flash, that's where your team mates come in. Somebody else engages and you go in after. Otherwise you can also flank them or attack them from the back once the team fights come. Don't engage first cause you'll just be blown up because Riven is very squishy.
As for match ups, that's what's great about Riven. There is no hard counter to her per say as long as you know how to use her depending on her opponent but there is obviously some harder ones to play against. Guys like Kennen who just pokes her to death and can escape her is quite good. Renekton who is a bigger lane bully than her is also a great counter to her. You can deal your damage before Riven can even retaliate due to your kit. Irelia is also a good one but it's a bit of a skill match up rather than a direct counter but generally you have the upper hand. Other counters include Garen, Malphite, Quinn, Olaf and Pantheon. Of course it's not like they hard counter Riven cause once you get past early game safely, Pantheon becomes a joke to you. In these types of match ups where you constantly get harassed, I usually max E(shield) so I can survive the early game and outscale them mid game. As a rule of thumb when picking against Riven, the best ones are always the ones who can out sustain and out poke her. Riven has the worst HP5 of any champion of the game so sooner or later she has to back when you harass her. Poking her down from a long range is bad for Riven cause in order to do trades she has to either use her dash or her Q which lowers her EHP since the shield only last 1.5 seconds or risk using her primary damage dealing skill to gap close meaning she won't be able to do any meaningful damage to you once she reaches you.
Ori is a great pick for mid because I find that she fits any kind of team composition and meta. Although I won't necessarily take her top or supp. Not top cause she has no mobility or sustain and not support cause I find her inferior against other supports although you can. Lulu is also good cause she can be a flex pick and can go top/mid/support so once you start learning her, it's like you're learning 3 champs at the same time.
If you have any difficulty on some match ups with Riven,Renek or Irelia, I'd be happy to help as I've played them tons.
Edit: I forgot to say this about going against Riven. Once she uses all of her skills, DO NOT BACK DOWN. Retaliate and deal some damage to her as well. She can't fight back cause she used all her skills. Her AA has shitty aspd so she won't deal a lot of damage and she used all her skills to get to you so she has to walk away. Her cooldowns are still pretty long in the early game so use this to your advantage.
Edit2: I forgot to answer your questions about top lane champs that compliment her. For team composition you generally need a carry, a tank and an ap. So if you count Riven as a carry and Rumble as the ap then you just need a tanky champion to with it. Now for top lane compliment with Riven, you just need someone you could deal with her weaknesses mainly sustain and poke. So choose someone who is strong against poke and/or sustain. I myself chose to use Renekton and Irelia instead because I like how they counter each other in my opinion. I feel confident enough in myself that I can deal with Riven's glaring weaknesses that I don't feel compelled to master any more but if you want to have maximum efficiency then IMO picking someone who can deal with sustain or poke can be good. Better yet pick someone who has sustain and poke. Poke doesn't have to be range specific. It can be someone like Renekton who can dash in stun and then Q to deal damage and get out with another dash before someone can trade. I guess I contradicted my earlier statement lol. I think Jayce would compliment her well.