I like the Yogscast for their Tekkit videos but I cannot stand them on their own. To me, Simon and Lewis are only tolerable around Duncan, though Sjin is pretty cool as well. I'm not a huge fan of stupid humour, the kind where people run around without thought to what they are doing and often get hurt as a result, and that is basically what the Yogscast run on. Duncan is wonderful, even if he is monotone, and I can't stand Sips, and Hannah is very lovely to listen to. Sjin I can't watch on his own because his voice is a little too high pitched on my speakers, it makes him sound really weird, but it is only with his voice.
DireWolf is a pretty great guy, he does well with his mod spotlights, but I feel he takes too much time to get around to doing things. I often skip episodes in his series just because I don't watch to watch 40 minutes of him building the same thing. That being said, I can see why his videos are often seen as tutorials and I owe my logistics system in SSP to him.
All in all, I'd say the Yogscast has a higher mainstream entertainment value, while Dire has more loyal fans and less hate. To me, they both are going to lose longevity if they don't start trying new things, but I enjoy both of their content. I do prefer Dire's, but the Yogscast has an entertainment value when I'm sad. I'd say you can't compare the two, because they do completely different things, but if I had to choose someone to watch, I'd probably pick Dire, as I find his voice soothing and his need to call things "awesome" and "cool" rather adorable.