This is an interesting question, especially as I am questioning the value of the beast lately.
Here are some interesting stats from FUMBBL Blackbox :
As you can see, even though Nurgle trend up at higher TV, they still don't do as well as Chaos.
Now sure Chaos Warriors are better at winning games than Nurgle Warriors(although not as good in a fight) and Beastmen are a lot better than Rotters, but I think that maybe one of the reasons they don't do as well in a matchmaking format is because of the Beast.
Even though I class him as one of the best Big Guys in the game, in this edition big guys are quite a liability.
Giving him Block and Dodge is 200TV and that's a full clawpomber.
I personally would consider firing him and doing without in an online matchmaking format if winning is your primary goal.
If you decide to keep him Blodge Guard SF is cool but thats a long way off and by the time you get that your team will be high TV and opponents will have T-C-Pombers to take care of him easily.
I guess I would take Claw on him and kill stuffs more.
Dirty Player and Wrestle are definitely the skills to choose on Rotters.