OKI, first thing first: MT4 and MT5 aren't some trading strategies, they are both trading software - meaning a software which allows you to buy or sell currencies ( of course if you have a trading account and money in it

).
A strategy means a set of information sources ( be it indicators, fundamental analyses sites, different market reports - like COT -, movement of planets ...

- it's for real, it isn't a joke - ) which allows you to have more gains than loses, so that you will not entirely lose your account by trading it.
And to answer your question, I would go for MT4 at the beginning, because what matters for any software in this world is the ecosystem - meaning how many people is engaged in development of plugins ( like the indicators in our case ). But also MT5 is catching up the pace ... It's just that MT4 ecosystem is older, this means bigger.