Best bang for the buck would be the D3200 or D5200 because they'll offer 90% of the experience for 75% of the cost. The differences between the
D3200 & D3300 and the
D5200 & D5300 are not extraordinary but still noteworthy. The biggest area is the video abilities between the generations - nearly everything else is simply more refined.
The same goes for the
3x00 & 5x00... Differences are pretty minor but so is the price difference (relative to cameras). The D5300, for example, has more auto-focus points (very helpful), GPS (value depends on how you use your camera - great for travel), and flip out screen (seems gimmicky until you see how obscure angles can totally change/improve a shot). Its a $200 difference between them. If that difference doesn't bother you too much, and you think you may appreciate the added features, then the D5300 is the best value. Not bang for the buck, per say, but best value.
IMHO, If I started acquiring gear all over again, I would start with a
D5300 Body ($600) and a
Nikon 35mm f/1.8 ($175) lens. This would give you nearly all the benefits of current generation DLRS and a fast lens that will give you the most artistic flexibility on a budget. The only downside to the prime is you will have to zoom with your feet.
ETA: I currently use a D5300. Its my fourth Nikon body in 8 years (upgraded for the video capabilities). Very happy with it. Id love to go FX some day but there is no value in it for me these days... keep blowing my photo budget on $1-2k lenses and other equipment instead :)