Only you can answer that, they all have their subtle quirks.
In general, mainly due to spread costs, and they are the most traded pairs,
EURUSD and USDJPY are probably the best starting point.
Just my opinion though.
Having a favorite market to trade is much like having a favorite pizza. It's just a personal choice.
I don't know if AUD is my favorite because it has been a money tree for me or because it is at the top of my list of markets to analyze each day (it starts with letter 'A'), but I have been trading AD futures and forex for so long that I just like it.