I think it is time for some facts. The .224 Valkyrie due to its size does not offer much in realm of bullet expansion. Next at what range are you going to try to bring down you deer?
The .224 Valkyrie has a average bullet speed of 2700 FPS(feet per second) at the muzzel the bullet has 1457 Lb Ft of force.
The .308 Springfield round has a bullet weight of 150 Grains the Valkyrie bullet weight is around 90 Grains
The .308 leaves the muzzel at around 2822 FPS. with a force of 2822 Lb Ft. The .308 bullet is designed to expand making a large wound channel and a faster kill.
In my opinion since you are new at this hunting thing you amy want to give yourself the best possible advantange. Go with the .308. If you like the AR platform go with an AR 10.
Just an opinion.