Here’s the thing: You’re asking what you should do so as to become competitive. I’ve got experience doing exactly what you’re trying to do now: buy better characters so you can win more.
My bad luck is that I invested in Spider-Man, and though his stun-lock trick earned me a lot of good covers, the party ended, and my money was lost. Around that time, a replacement Y/B/P character arrived, and he seemed pretty amazing. I set my sights on Falcon, and told my friends to do the same.
Anniversary time, a friend and I each bought a Stark Salary and maxed our Falcons. It turns out, he wasn’t nearly as active a player as he seemed all the times I had my ass handed to me. Nor was 


Daken, who I remembered being a lot more dangerous before. Come to think of it, I remember pretty much every new character being pretty hard-core in that one node in their first PVE where you play a 4/4/4 level 100 version, and just cook the enemies before you’d even gotten warmed up. I think they have a trick for stacking these matches to make the new guy seem really cool. They managed to make She-Hulk look cool, and I can’t remember anyone doing that since.
Next stop, Sentry. Everyone talks about how Sentry is the Answer, so I knew he was a character I should have pumped. Problem is, playing Sentry is about as fun as playing Spider-Man used to be. It’s why they nerfed Spidey: this game is supposed to be about strategy, not tricks you repeat by rote. A few boosts, a fully-leveled Sentry, done.
A lot of my friends don’t even want Sentry because they hate the idea of harming themselves. And they have a point. He can get the wins, but he’ll ruin your roster, use up your healing, and leave you waiting for the next time.
By all means, spend your money on Hero Points, and spend those Hero Points on the two most obvious killers in the game. Of course, you’ll be risking that nerf they keep talking about. Might happen. Might make him a competitor. Might make him a loser. You’ll get easy wins right now. But you don’t necessarily want that.
I like X-Force. He’s too tough to fight. If you want to make a strong character, he’s one to get. But he’s not the only one. Thor is currently the top character. You might want to get him.
If I could take back my Hero Points and respend them, I’d skip Falcon, Daken, and Sentry. Maybe. But I know I’d want all my Thor covers and a maxed Rage of the Panther. Or now that Blade is around, I’d keep Falcon and Daken, but make sure to max his stuff, as well.
I guess the point I’m making is, the pleasure of this game is gaining on the characters you can. I think if I put $10,000 into it, I’d have bought myself out of all the remaining play value. And if I’d listened to the popular opinion, I wouldn’t have my own winning team. I use GSBW, Human Torch, and The Hood. They’re great. But of those three, only Hood ever gets rated highly.