Surely a pixel is a pixel. It's just one 'blob' of light, isn't it?
Well at least that was how I tried to convince a colleague of mine, many years ago. What I didn't realise was that his pixels were "bigger than mine".
This didn't really seem intuitive. There are, after all, so many of them. Does it really make a difference?
I was certain, in an obstinate, unendearing way, that my 18Mp (crop) camera should be as good as a similar vintage 18Mp full-frame model. Only I was completely wrong.
Over the past few years, I've rented the Canon EOS-5D Mark III, and owned the EOS-6D - twice.
The results have been remarkable. In good light my 7D would supply great images. I never had an inclination to pixel peep, the images always seemed sharp and crisp enough. However, in lower light situations (ISO 1600 or faster), the 7D seemed "barely adequate".
In contrast, the results from the 5DIII & the 6D, where used at the same event, produce results that are a marked improvement using exactly the same ISO, aperture & shutter speed.
Based on this experience, I would have to recommend the Canon EOS-6D as the perfect choice for an entry-level photographer.