Honestly I believe the Nikon D90 is the best DSLR available in the market on which you can actually learn photography. it is a truly amazing camera to start off and honestly I still love using this camera. everything about this camera is great. if you are planning of going professional then this would be the best choice as your first camera. once you truly master the skill of taking pictures in this camera shifting to a high end pro DSLR will just make you know your settings much easier and the high ISO will seem to come in easy use. one advice while using this initially its okay to use the kit lens but the rest of your kit try saving up and target the good fast lenses(24-70 f/2.8, 50 f/1.4 etc). if you are planning of getting a DSLR get the D90. you will not regret your decision.
One thing I should mention is that this camera has two main functions that I find to be really useful. this camera has a bigger body compared to the D3200 and the D5200 so if you have huge hands like me then its much more easier to hold and if it still isnt comfortable enough you can buy a battery grip. its really useful and the camera just feels really solid. second, this camera supports autofocus on the body. this allows you to use old lenses which do not have an built in autofocus motor. third. the camera has two separate dials that allow you to use one for aperture and the other one for shutter speed. I found this to be much more useful and comfortable than having to press a button and then scrolling to change the settings as found on the other cameras.