Brawny or Scythe

Which monster is the better s grade monster? Brawny or Scythe? I don't know which one i want to breed.

Scythe and Brawny play quite differently. Most people seem to use Scythe as a suicide attacker, whilst using Brawny as a tank. So it all goes down to what kind of play style you are after.
Personally, I'd go for Scythe, he's faster which gives you the upper-hand in most battles and his Martyrdom/Resurrect combo is lethal.
Brawny on the other hand has great defensive capabilities and hits hard, so he's great if you are looking a monster that supports your team with sandstorm for example.
So all in all, they both have merits, it just depends on your play-style and what you want his role to be in your team. To help you make a more informed decision, I've added a copy of their stats (level 50 S) and talents for you to better compare and verify for yourself whats best.
Cheerio!

Here's some pics of my Scythe & Brawny I actually like em both...