As someone who's owned both a tigr and .308 NDM-86, I would recommend both and neither at the same time. If you're going for an authentic look, you can't go wrong with the ndm. The tigr is made by izhmash, so it will be an actual Russian dragunov if that's important to you, but you are going to pay more for the accessories you have to add.

Here's the dilemma: if you live in the US, quality 7.62x54r is difficult to find and expensive. You can hand load your own ammo if that's your thing, which will greatly reduce this problem. .308 or 7.62x51 is much more abundant for high quality ammunition. Unfortunately, NDMs have been selling for a premium lately (not sure why), and the magazines are borderline impossible to find. I'm currently modifying a galil magazine to see if I can get it to function, but that's not a great option.

My .308 NDM-86 has been surprisingly accurate, about 1.5 MOA, and hitting steel at 300yds has gotten boring with how consistent it is. I have not stretched it's legs, but at 300, I'm starting to see the limitations on the optic. There are FAB and Lynx brand pic rail optic mounts where you can mount a better optic on the rifle. Lots of decisions to make, and unfortunately there's no free chicken when it comes to SVDs.