Both are good but as a saying goes 'old is gold'. Hence, we stick to MT4. One more reason is that you find many indicators coded for MT4 rather than MT5.
Both are good but I still prefers MT4 over MT5. MT4 is designed for CFD forex instruments, whereas MT5 is an all-in-one state of the art multi-asset trading platform, covering both centralised and non-centralised financial markets, including, stocks, futures and FX trading instruments.