Diamond is made by Bowtech, so they have some solid history behind them. I bought my son the Infinite Edge a few years ago and he has grown about 6" and 100 pounds, that particular bow is adjustable and has been able to grow with him.
I got the Cabela's Instigator for a little more than the Diamond, both ready to hunt. Once I started looking, the Instigator is the same frame by Bowtech as the Diamond, it has different limbs and cams. I will say, once we started shooting alot, we have upgraded the arrow rest (went with a biscuit) and the pin sight (got a lighted sight) and it has made a significant difference.