I know this won't pertain to all that many people, but it's something I've been mulling over for awhile. Cosmic Encounter is my favorite game, so I think about it often. One of the questions I got a lot is "what's your favorite power?" This list is meant to explain some of my choices and give some of my thought process behind the choices.
Fury gains a token for each ship they lose to the warp. They can use these tokens to add or subtract 3 per token from their side in an encounter. Fury has to play a balance game between ships and tokens, but if Fury is smart, they'll be a key player at the end of the game.
Genius wins if they have 20 cards in their hand. Often this is hard to accomplish, but certain flares can help. Genius does have the ability to forgo claiming a colony in favor of drawing cards. This gives Genius great flexibility. It is more powerful in a hidden power game, since no one really knows why you're accumulating the cards, but it's still a solid power, and a lot of fun to play.
Miser plays the game with 2 hands of cards. This gives them a lot of options when it comes to playing cards. They're still stuck with bad cards, just like everyone else, but they can also manage their main hand better, thus keeping flares and artifacts around longer. Miser isn't a power that's feared, and rightly so. It won't directly help you win a combat, but it does give you more options, and in a game that relies on cards to win the game, having more cards is a good thing.
Sorcerer has the option to switch the encounter cards that the main players play before their value is revealed. Sorcerer is a giant mind-game, which often leads to a Princess Bride esque moment that goes something like this. "I think you're the kind of person who's going to swap cards so I'll play card A. But knowing that you know that I think that you'll swap means you won't, so I'll play card B. But knowing that you know that I know that you know that I think you'll swap means you will, so card A it is." And so and and so forth.
Sorcerer lets you make something good out of the bad cards in your hand. It does require a certain finesse to use well, but it's also easy to play the first time you see it.
Pacifist is one of the simplest powers to explain, you win if you play a Negotiate. Now, you can still win an encounter the normal way and an N v N still leads to a deal. Pacifist is great because it allows you to utilize every card in your hand. There is that bluffing aspect where players don't know if you'll play a Negotiate, so you can slip in a low attack card while they go for the N to try to deal. Pacifist is a great power for using all the cards in your hand.
Remora is just a bit clingy, maybe too clingy. What I mean by that is Remora gets a card whenever someone draws cards, and a ship whenever someone takes a ship back. It means that they'll likely never run out of cards, and will likely never be low on ships. Remora continuously brings a supply of cards, which should help in combat. Remora itself won't help you in combat, but the additional cards and ships make you a bigger threat as the game goes on.
Chosen is the power I would pick if I had a "must-win" game of Cosmic. Chosen's power is to draw 3 cards after encounter cards have been revealed. He can then use one of the 3 cards to add to his encounter total, or replace the card he played. This has a two main uses. If things are close, you just gained a reinforcement card of some value. If things are way against you, you can hope for a Negotiate to at least take some cards from your opponent. Chosen isn't forced to add or replace anything, so his power can never hurt him.
Every power has good things and bad things to it. Different powers suit different play styles. Someone else's top 7 may be completely different than mine, but that's a good thing. I think every power (110 to date) has something to offer. Sure, you may not like all of them, but each and every power could come out victorious.