D5200 Vs D5100 which one to buy as 1st DSLR?

This is all well-trodden ground.  Nikon was stuck on 12MP for many years while Canon scooped up the gravy details with the 5DII, Nikon boosters all the while maintaining that 12MP was enough. Landscape photogs knew better, of course, lugging around 30MP monsters that cost a fortune or 4X5 view cameras.  When the D7000 came along, all the same stuff you're reading here to the letter was heard throughout the blogosphere.  Wasted pixels, pro glass required, massive tripod, mirror up, remote release, Teutonic shot discipline, etc., etc.  And let's not forget the necessity for a Cray supercomputer to process the file, and a server located in Finland north of the Arctic Circle to store the resulting massive amount of data.

Well it was baloney then, and it's baloney now that we're ready to take the next step up.  There's not the slightest doubt that everyone on this board who is telling you you don't need 24MP will be shooting a camera with that many or more within the next few years, easily processed with an i5 or higher with 8MB RAM.  I suggest, (and I realize it's not a popular viewpoint) that you start with a higher res camera to begin with. Digital is pretty cut and dried.  6000X4000 beats 4928X3264 hands down for detail.  If you have the 24MP item, you'll be in some very good company indeed for landscape use.

The OP will not go far wrong choosing a 16MP camera, but he will get a sharper picture with a 24MP without having any training at all.  OP has opined (sorry :^) that he would like to shoot landscapes.  If I had ten dollars for every shot I took with my D7000 that I would love to reshoot with the D800e, I'd be kicking pink sand in the Bahamas by now.  There simply are not enough pixels contained in 4928X 3264 to do a really superb job of sorting out dense foliage or a distant ridgeline to the extent the human eye can do with ease.  The difference between 16 and 36MP is night and day for such fine detail, easily visible on any decent monitor or a print of any size. 24MP takes you a good, disproportionate percentage of the way towards really high quality landscape resolution.  For shooting people, you might as well be using a V1 for all the difference it makes.

We are about to enter a new, very high res area of monitor performance as well.  A 4K monitor will be coming to a laptop or desktop near you in the next few years:

http://www.tomshardware.com/news/Intel-Higher-Resolution-Displays-Coming,15329.html

I've been doing the digital thing since inception, and we thought 2MP was plenty when all we had was VGA.  Hot stuff back then, but pitiful, grainy mush now.  I prefer to future proof my files.

The whole printing large paradigm is time tested and certainly will never go away, but it's getting a bit long in the tooth.  I think the default delivery system of the future wil lean heavily towards a 4K 50" or bigger flat panel TV in the living room within a fairly short time.  1080p already looks damn good, 4K should be a jpg machine par excellence.

Have a look at what 24MP can do for you in terms of seriously increased microcontrast and rendition of detail:

http://masters.galleries.dpreview.com.s3.amazonaws.com/2350236.jpg?AWSAccessKeyId=14Y3MT0G2J4Y72K3ZXR2&Expires=1355421326&Signature=xIoxiAURx3R8LGxODnzb53ETXOo%3d

The D5100 can not do this, period.  The D5200 should be pretty close.  While you're in the neighborhood, have a peep at the rest of the samples in the collection...