Loki... 

Wait for Sir Alfred or David the Legend to give you more info and advice.
Don't worry there is always uniform sales on special events.
Cap. America uniform is worth to buy if you keen to use him.
With the correct gear and ISO set, he can clear all the stages.

You can refer to the Hero Ranking button in the front page of the game.
There you can see the most popular heroes used in MFF.
I would say (in no particular order) Female Loki, Silk, Hulkbuster, Carnage and so on.

I would focus on Warmachine as my first strong hero since he clears most of the special missions really fast (esp Giantman). Ironman is also a strong early game hero too. Spiderman is easily farmable as well.

Cap America is easily farmable too but u need I Am Also Groot set and strong ISOs to make him really stand out. He's more of a late game hero.

Yea I admit I bought Loki's bios too.. if u can afford the crystals why not. Save the hassle on farming his rifts. Oh the Lady Loki uniform is must too for PVP Arena. Another strong must have hero that can't be farmed is Silk.. if wanna buy get her bios.. will help a lot in PVP and everywhere else.

If you can get Jane to 6* and max out her gears, she can clear any stage quicker than most other heroes.

If you're looking for farm-able heroes, then what Davidtcf said can be taken into account

incase you get further confused, the rank up ticket i believe is not a mega rank up ticket where they'll take your hero from any star to 6*
you can only use the 6* rank up ticket if your loki is at 5*, you can't use the 6* ticket while your loki is still at 3*

some characters are weaker than others.. as long u make sure before you use them then it'll be fine.

I don't recommend using any tickets/free bios ranking up farmable heroes (except for Rift only heroes) as they can be farmed everyday till maxed out (6* + level 20 gears).. will only take a few months to do so.

I've been playing for a year.. all my farmable characters are now 6*. Some are even with maxed level gear or level 18-19 gears.

Yes, most of the member here are in the same alliance.

Use the ticket on Loki, use the bio sub for his gears, once you have him maxed, you can handle every single part of the game technically speaking.

You'll need a lot's of 6* heroes to join in.
If i'm not mistaken at least 5 > 6* heroes.   

they won't be easy. Even with Max out teams it's still possible to fail and may require several tries.

Best character in WB is Ronan as leader paired with a max out Floki. Floki is very effective in clearing WBs.

yes, but Jane's bios are not farmable.. need to use rank up tickets, bio selectors, or from daily free chest.

Jane is stronger than Black Widow due to her 6th star skill being iframe (enemy cannot aim at her for a duration). And easier to boost her attacks too with a +% lightning damage booster.

I have a 320 bio selector and a 3-star hero selector. my current team is floki 6-star and ant-man 5-star. any suggestions who to add to my team    and how to spend the selectors? 

Spade7 is silk really good? can you suggest other heroes 

yeah that is avengers alliance.. right now version 2 d. but i dont like coz too much manual play required.. not my thing anymore dont have the time to grind 

that time Fox and Marvel havent feud till so terror... it is after Avengers 1 and 2 that Marvel studios became disgruntled with Fox.. likely due to quicksilver and scarlet witch.. Fox threaten lawsuits etc etc... and doesn't want to share. Padahal those characters in the beginning were made by Marvel comics   

yea until the point Fox learn to bow down and apologize and work together with Marvel.. Marvel will remove all Xmen and FF4 related content from games and toys and nowadays even killing them off in comics.. that's how bad the bad blood is for both of them    Marvel wanna choke Fox slowly till they die.

Finally, Marvel also dislike the creative direction that Fox does with their movies (since the license agreement is once a movie every 5 years to retain the license) Fox cincai make Xmen and FF movies all the time just to extend their hold on them. See what happened to Amazing Spiderman... Sony cincai make the movie end up became a flop.. just to retain license.

But Sony smart la... they realize things are going bad with Spiderman franchise d... and learned to share.. so that's why cooperate now and "borrow" spiderman to appear in Civil War - the barter is ironman to appear in the first Marvel-sony Spiderman known as Spiderman: Homecoming. That movie will likely be great with Marvel Studios lending their expertise  Good for both sides ma if the movie works and rake in big $$... Marvel will have some share but I don't think that is their main aim... their main aim is to protect the good image of their IP : Spiderman... movie good = comics will sell well also.