I'm having a tough time deciding: Mundo or Nasus?
Mundo. He's more straightfoward and easy to play then Nasus, altough nasus isn't bad either. The problem with nasus is that he's a weird tanky DPS thing that needs to farm alot, altough his team usefulness is about the same. He has a baws slow ability that is one of the best in the game since it slows both movement and attack speed and is actualy pretty long. His ultimate and renekton's are almost the same. The disvantage is that you need to last hit aloooot to charge up his Q and that he needs alot of mana to use his abilities well. Its a perfect spell to use with sheen/trinity force though, and it can crit too. I remember hitting as high as 850 with it a few times with a trin force powered crit. Trin force is the only attack item you usualy take though, not a big fan of DPS nasus.
He also has the sexiest voice ever.
But yea, people will cry less if you pick mundo.
My thoughts on this:
I don't know how much Nasus can act as a DPS, but I doubt as well as Mundo. Mundo is actually a tanky DPS rather than a real tank: Q allows easy chasing, W allows him to deal continuous dmg when he is bashing his enemies and also reduces amount of slows/stuns etc. E is basically Dr. Critdo's best thing ever, without any items that give AD it is possible to get +150 dmg from this. R makes chasing easier and heals him of course.
DPS Nasus needs farming for his Q as all Nasuses do. DPS Nasus just needs more. His slow is godlike for the purpose of a DPS as it is very long duration and very powerful as well. His AoE farming ability reduces armor so it can be used to make killing enemies much easier. His ulti also gives him AD when enemies are nearby.
Those are my thoughts on building them DPS. For tanks, Mundo can survive well, but he lacks what a tank really needs to do in the team. Focusing on him is highly discouraged since he pacs no CC besides Q's slow, and he heals himself to full hp anyways so why to bother attacking him.
Nasus has his slow to allow chasing/escaping, which can get your team kill/save an ally. It reduces attack speed so works well against physical dmg carries. E reduces the armor of all enemies in it, so works well if your team has physical dmg.
So whichever you pick depends on how you wanna play them. AS Dakk said, Mundawg is more straightforward and "acceptable", but in my opinion Nasus is more useful for the good of the team instead of just himself.