Canin EOS 70D or Nikon d5300?

Just to clear up Andrews point first. The Canon 70D can use, meter and autofocus with every Canon EF and EF-S lens made in the last 30yrs. I use a 1986 EF 50mm f/1.8 Mk1 on my 70D. The fact that Canon completely changed their lens mount in the mid 1980's is water that has flowed well under the bridge by now.

Of the 2 cameras you list the 70D is the higher spec. Nikon competitor to the 70D is the 7000 series. The 70D body is weather sealed you need to get L series lenses to get them sealed too.

I have a 70D and am delighted with it. Full frame is not a holy grail but should you want your Canon lenses to fit at a later date stick with EF lenses. EF-S lenses are crop sensor only.

You can use any dSLR to shoot anything. Lenses made specifically for crop sensor bodies won't work with full-frame cameras (and will damage them even).

The 70D is mid-level and is far much better than the D5300 which is entry-level. The 70D would be more comparable to the D7200 while the D5300 is more like the T5i. Anywho, they're all basically the same. You will get the same picture whatever dSLR you use. That's because picture quality depends mostly on your skill. The camera is only a tool.

The Pentax K-50 has weather-sealing and a pentaprism (brighter) viewfinder, meters with legacy lenses (the Nikon won't, the Canon can't even take them), and costs less than the EOS 70D.

Canon's direct competitor to the D5300 is the EOS 700D/Rebel T6i, which is no match for the Pentax on paper.