In my personal experience, Epson printers with six colour cartridges are the ones to beat in terms of resolution, colour rendition and quality of printing. Naturally they work best with genuine Epson cartridges and paper and it is not cheap running off prints at the highest quality. The printed images are reckoned to be good to last up to a 100 years though.
For day to day colour prints I use HP printers. The specifications are rubbish compared to Epson, but they do the job relatively cheaply, with okay quality.
A3 sized prints should be fine with 15 megapixels. It is possible to use computer software to increase the number of pixels and colour them with interpolation so that the image appears softer but without any obvious pixelation for even larger images.