The Marvel Future Fight Best Team can vary slightly when it comes to Nord Stones, but for the most part Heroes are very different when it comes to gear and leveling. There are of course some that are much better than others. In the long run your gonna want to have many character that are build up, not just a group of your favorite 3. This will be especially important if you plan on making use of the Villain Siege.
While playing the Arena I have noticed that the Hulk and HulkBuster are the toughest opponents to deal with. Even when they are 5 or more levels less than my guys they still put up a good fight. As you can see from the chart below they both have the highest base HP out of everyone and there base attack power is just below the best.
So for me, I’m pretty sure that one of, if not, the #1 Marvel Future Fight Best Team would be the Hulk, HulkBuster and Thor as they all go together in the Team Bonus area. I think that Thor would be the weakest link, but there is only one combination that include both the Hulk and Buster called Blunt Force.
When your done here check out the MARVEL Future Fight Wiki, Guide and FAQ for a ton more related content to help shed light on thing.
Marvel Future Fight Best Team
Using a group of Characters that get extra bonuses when together will offer huge benefits when it comes to survivability and DPS. You will unlock an extra skill that can be used during battle to combine all heroes attacks into one high damage move. The countdown timer will be much longer than regular skills. Then, when switching party members in battle others will appear for a quick extra attack. You will also get special permanent passive buffs that can be viewed on the Team Bonus screen.
Using a group where all members belong to different types like Combat, Speed, Blast and Universal. This way they will have their gear upgraded faster from a mixture of material colors found on mission completions. Instead of having 3 Combat units that all take the same material to upgrade gear, then having to play the same missions over when the other color materials are going to waste. Many of the top Arena players seem to use this tactic. Choosing people who can have their bios found easy and in big numbers is key also as some can take forever when compared to others.
This chart show the max out numbers for all heroes and only includes Rank, Level and Mater. It does not take into account stats from gear, Stones, skill and other upgrades. You can find this info in the MARVEL UNIVERSE menu. This Best Hero/Character post has more information that you might find useful.