Ok to start off this is just my opinion and I would love to know what you guys think! They did a pretty decent job balancing heroes in 5v5 and almost all of them have a place in 5v5, but some of them seem to have taken to it much better than others and I want to list them here!
So to start off we have the most obvious in my opinion:
CP vox. He has good team fighting, wave clear and good lane harass… this makes up for the fact that he cant quite 1v1 an enimy wp carry. He also has mobility that alot of other cp carries lack this combined with an ult that can destroy teams makes him an exelent top or mid lane pick (bot works but then he will be farther from the cp buff)
CD fortress fortress’s ult is of course impactfull in even in 3v3… but in 5v5 it absolutly dominates. but that is not the only reason why 5v5 suits him. CD fortress is also able to give his whole 5 man team decent lifesteal AND move speed towards a carry that you know is about to be deleted 
. Also with a cheaper SGB and a much better SC than last patch he has a much easier time hitting his lvl 6 power spike than before. (Neat little trick I have found is if you have a team that dives with you when, you can abuse the fact that you are not the priority target you can get away with 4 damage items if the enimy team is skewed towards 1 damage type like 3 CP and 1 WP) I personally belive he is the strongest jungler in 5v5 atm
Here is a good example of what I was saying about an extra damage item In this comp I knew they were going to try and focus SAW and ignore me so I got a fountian to try and keep him alive with phinn but I also got a 4th damage item so I would be a little more bursty and be able to ult spam a little better. A decent middle ground is getting a utility item like nullwave or super scout because they give yoi CD and health so you can be tankier and spam your ult more. (Ps this game craked me up because phinn warning pinged the minions every time I came to lane and he has 30 cs XD)
Flicker you can spend all day just dominating the vision game and ganking lanes. His ult is also super usefull for creating awesome team fights in 5v5 since vision is harder to maintain in 5v5
Taka the burst damage and the stealth in a game mode with more diffucult vision and plenty of squishy laners.
Churnwalker having the opertunity to get 5 people chained and 5 people damageing chained targets=tons of tankyness and damage. Ofcourse churnwalker is an incredibly diffucult hero and for him to be broken you need to have skils I do not possess. (Basically you need to either be a god or FlashX… if there is a differenece 
)
Lyra she can’t keep people healthy through constant dps and massive burst heals like she used to but her ability to just keep all of the people in her lanes topped off helps her team come out on top during the laning phase.
Glaive awesome split push, gank, and teamfight utility with a couple SSWs! This makes him an exelent bot laner or jungler.
Koshka her buff to her B makes her an exlelent brawler in 5v5 and also moves her slightly in the direction of a bruiser. And with such a big map using her ult to single out a target in a lane for a gank is not the death dentence it often was in 3v3.
Samuel sam was kinda undervalued as a laner in 3v3 where porting home amd then coming back to lane was often not a big deal. In 5v5 his ability to outlast the enemy laner through poke and his perk for sustain is extremely valuble in 5v5 and allows him to take turrets and push people out of their lane… The current interation of clockwork also allows him to use drifting dark almost constantly so he can use it for farming as well as fights.
I will update this later with more heroes be sure to comment which heroes you think are strongest!