My pup gets bored of food quickly so I'm almost constantly changing his combo. Lucky for me, he doesn't seem to have too much of a sensitive stomach. Of course you want to be careful if you decide to switch, your pup might get loose poops or diarrhea. yuck.
For dry food, I started with Taste of wild for puppies (did both flavors, he liked chicken better). Then moved on to Wellness grain-free for puppies, and now I'm feeding Evo Food grain free- chicken (also tried both flavors, and again puppy like chicken better). Evo Food is great, really really high in protein (like almost 50%) and calories (about 500 cal/cup) so you end up feeding less cups per day and save money in the long run.
For wet food, I started with Honest Kitchen mixes. They're great, just hydrate with hot water! Also, it's human-grade food with veggies and protein. They use fancy things like cage-free chicken and grass-fed beef. (Sometimes I wondered why I bought my dog better food than I feed myself...) My pup liked it for a while, but eventually lost interest and it's super expensive.
Now I just buy different flavored canned food and mix it into his kibble. I usually go for cans from Wellness, Halo, or Merrick. I really like the 95% stuff, it's mostly just additional protein but I'll give him stews as well so he can get more veggies. This way puppy gets different flavors added to his meal so he's not bored. He still like chicken best.
Usually I'll feed him maybe a quarter can of food a day and 1-2 cups of kibble depending on how active he is. My pup loves it and he has healthy poops. =D