Spoiler Fire Emblem Awakening, Perfect Ending Help

[Chiraku]

I got my 3DS a short while ago and have been playing Fire Emblem Awakening, and I am right before the end, and I am aware there are multiple endings, but I haven't been able to find concrete answers through my searching (and I've been wary of spoilers) for which is the 'good' or 'Best' ending. Towards the end of the game, the avatar is faced with the decision to sacrifice himself to destroy the big bad. I understand one ending is to have Chrom finish the big bad off instead, but I'm unaware whether is is the good ending or not. The one I've heard the most frequently is how you have to have all the unit's on their highest support levels, or at least have the Avatar's support levels with everyone at their highest.
So... which way to the best ending? Is it both? Am I missing something?

 

[Keeseman]

Having the Avatar finish Grima off is definitely the most satisfying ending. But don't worry, if you want to see the other one, you can play that battle over again.

 

[Chiraku]

Alright. What about support levels? Are they important?

 

[TriFiERCE]

Don't you trust your grocer? lolz

((Note: This is not spam, I am Chiraku's personal Game Grocer))

 

[Chiraku]

Allow me to re-state my question; Do you need every unit to have the highest support level with eachother or just the avatar for the good ending?

 

[Keeseman]

You should probably have a wife for the best ending, and have some other characters with S levels, but it isn't necessary. For example, my character's level for Chrom support was only a B in my first time around, and the ending was still pretty sick.

 

[Ventus]

The best ending is simply the Avatar defeating Grima. It starts off bittersweet, but you get a healthy surprise after the credits run their course. Support levels are not at all necessary.

 

[Chiraku]

Alright, thanks alot!
On to the finale!