If I had to choose just one, then it would be eurusd undoubtedly and thats because its one of the most liquid pairs and i get spreads as low as zero with fxview on this pair.
Talking about the second part of your question, majors are the most suitable for beginners. In fact I have seen most people start with eurusd since its one of the most stable currencies to trade. So, that should be a good option for you too.
for me XAUUSD most volatility Forex Pair / Metal ... sometimes its crazy huh, but usually if you use Fibo levels and Elliot Wawes ( at this instrument they works )- you in profit with corect low risk ) love it