If you are not going to invest in more lenses and do not need the swivel screen, then in my opinion the D3300 with its kit lense is and excellent buy. It is much cheaper than the D5xxx or D7xxx, much lighter and the battery last more. All in all it is an excellent camera to carry around. What you will not get is
. Swivel screen - D5xxx
. Dual cards - D7xxx
. Metering with non cpu MF lenses - D7xxx
. AF with "D" lenses - D7xxx
. Marginally less DR - D5xxx, D7xxx. But nothing to speak of
I have a D300 and bought a D3300 in March, and am loving every moment with it. As I had quite a few lenses, 2 flash and a tripod and other equipment, I did not have to invest beyond the camera. Had I started from scratch I would have bought an FF body.
In my opinion, if you are going to shoot wild life, then you need a good high ISO capability. In that case a D750; even though quite expensive) will shine. You will also get all that is lacking in a D3300 :
. Swivel screen
. Dual cards
. Metering with non cpu MF lenses
. AF with "D" lenses
. More DR
. One of the best high ISO capabilities
As things stand today, you may save a bit on a body by getting a D5xxx or a D7xxx, but the cost of lenses remains same. As time goes by your investment in lenses will be many times more than an expensive body. At that stage you will wonder why you compromised on a body, which saved you quite an insignificant amount invested in the whole kit.