I think MKG is the best player for us to take at the 4 because he is the type of player that would most contribute to longterm success. Sure, Beal may land on more all-star teams, but if MKG gives us more upside in terms of winning in the playoffs then I would rather have him than Beal.
The main thing that makes him desirable is his work ethic and what Bill Simmons calls "winnability." He seems to have the mentality that would allow him to contribute to said winning and also allow him to become a leader on this team. Having a great relationship with high-school teammate Kyrie is just the icing on the cake. His work ethic should be sufficient to solve any problems he has with his game.
And finally, to address the concern about his lack of a jumpshot, I have two points:
First, we could roll out shooters with the capabilities of Ray Allen at 3 spots next year and we still won't win. The next season isn't when we are supposed to make a jump into th playoffs. It is when we continue to let our young players grow, get assets, build chemistry, and prepare for future domination. Thus, in no way is it counterprouctive to trot out a rotation with MKG, T^2, and AV getting big minutes. We don't need the floor spaced now. If we need floor spacing down the road, then we can draft/sign players to fit into the spots. In the long-term, I would fully expect either T^2 or MKG to turn into quality outside shooters for their position (18 footers for Thompson, 35%+ from 3 for MKG). With Kyrie's awesome shooting numbers we just need two more players with decent jumpers to fill in the rotation and we will be set.
Second, it is possible to shoot well with an unorthodox release. Someone earlier posted the percents for Marion as he shot pretty well for his career despite a shot that is about as pretty as a pig wearing lipstick. Heck, even Kevin Martin has an odd release and he is a constant threat from three point range. There is no reason that MKG can't either a. fix the release or b. develop his odd release into a consistent one. As long as the ball gets into the basket, the method is really irrelevant.
So, I think that we should draft MKG because he is the kind of player that fills in all the holes for a championship team. Whether that means he is a rich man's Horry or a poor man's Pippen/Havliceck doesn't matter. As long as he can contribute to the acquiring of championships, it is set. This is where I think he differs from the other possible options at his pick as he is a player who has the skills to excel in the postseason and not the regular one.
Do I have any way to back this up beyond what I have seen of his play and read about him? No, but everything I have read would suggest my conclusion is correct.
tl;dr: MKG helps win in playoffs, jumpshot isnt an issue