I have been feeding my dogs Purina Pro Plan for years, as have many people on this forum, with excellent results. It's a good food, and I'm sure that some of the other ones are better--there is always something better--but my dogs do well on it and I have to no plan to switch.
I think your little guy looks slender but good in the picture, but you are the best decider because you can put your hands on him. You could up his food a bit with no problem. GR puppies are so active that he'll wear it off. I fed Tucker PPP puppy until he was one year then switched to PPP sensitive skin and stomach. I have Bella switched to that now, also and she loves it. I'd have Tess on except that she requires a prescription diet.
Here is a body chart and instructions to determine if your dog is the correct weight (note that it was done by Purina...). How to Tell if Your Dog is Overweight, in Ideal Body Condition or Too Thin
Here are 3 simple ways to tell if your dog's diet needs an adjustment.
Rib Check: Place both of your thumbs on your dog's backbone and spread both hands across his rib cage. You want to be able to feel his ribs. Actually feeling your dog is important, as the coat of many dogs will make a visual check difficult.
Profile Check: Examine your dog's profile – it’s best if you are level with your dog. Look for the abdomen to be tucked up behind his rib cage - this is ideal.
Overhead Check: Looking at your dog from overhead, identify whether you can see a waist behind his ribs. Most dogs at a healthy weight should have an hourglass figure.
If you find that your dog's ribs and waistline aren't where they're supposed to be, adjust the amount of food offered accordingly. And here is their chart: http://www.purinaveterinarydiets.com.../dog_chart.pdf
The best advice I've gotten on this site from long-time dog owners and breeders is to find a food that works for your dog and pocketbook and stick with it.