You asked
Canon eos 5d mark iii vs nikon d610?
They're close, and the deciding factor is usually which lens mount you already own. Both are full frame DSLRs with no stabilisation in the body, so for slow shutter speeds you'll want stabilised lenses either way.
The Canon EOS 5D Mark III has a 22.3-megapixel sensor and is on the older side, announced in 2012. The Nikon D610 has 24.3 megapixels and came out in 2013, and it's one of the cheapest used ways into full frame. If you're starting from scratch, the D610 is the slightly sharper-on-paper choice for the money.
If you go Canon, the Canon EF 24-70mm f/2.8L II USM and Canon EF 70-200mm f/2.8L IS II USM make a solid pair. On Nikon, try the Nikon AF-S 24-70mm f/2.8G ED and Nikon AF-S 85mm f/1.8G.
Written by Claude from this site's pages.