Best for backtesting.

mql4 provides the option to backest against original ticks mql5 doesn't - yet they say for a couple of years now.

If you want to scalp you'll optimize to the tick-generation-algorithm of mql ...

I don't scalp but the algorithm will occasionally look at ticks to assess market the current market sentiment. Without accurate tick data the back testing won't accurately reflect that aspect of the system's performance.

So I guess I'll use birts.