Cornish/Rock like stated above are the fastest growers for meat, but with how the chicken market is now... You might not find any chicks or it'll be months before you can get any from a hatchery. Many places have a long waiting list.
I prefer Dual Purpose (DP) breeds. You can get breeds like Delaware, Barred Rock, or pretty much any standard size chicken breed. DP breeds can lay eggs or be used for meat, which is why I like them because I keep the females for eggs and use the males for meat. You won't be able to process a DP breed early like you can with cornish, but waiting till 12-20 weeks is well worth the wait. When you process them you will want to let them rest in the fridge up to 5 days (I prefer 5 days) so that they have time to get tender. Then you can bag them then freeze or you can cook them. I prefer to cook my DP birds in the instant pot then I put them in the oven on broil to crisp them up a bit.
If you are looking for flavorful, it would be DP birds or heritage breeds. Cornish are the same a grocery store chicken and are quite mushy and flavorless.
I like to use rubs on my DP birds before I vacuum seal them to freeze. It really makes them shine when you cook them. Sometimes just some salt and pepper will do. We like making our own rubs.