Which currency to trade during London trading hours

I is always better to focus on one trading pair and study it to perfection. This way you will be able to understand pair behavior much better and you will learn patters that repeats on the trading pair.
When you know patters that repeats you can base your trading strategy and get profit from it.

Here is a chart with daily average pip range so You can check what pair is most volatile on London trading session.

More information you can see here: https://getknowtrading.com/forex-mar...ading-session/

Trade all major GBP pairs and major USD pairs, in my opinion, especially the former.

Basically, traders need to select their trading pairs based on their practice result. By the way, I am also comfortable with the major Forex pairs.

Another factor to take into consideration is when these currency pairs are most active (i.e during which sessions) and when you, as a trader, have the time and energy to do so. If the trading session you want to trade is in the middle of the night and you're simply not awake enough to trade it consider picking another.

Session based successful traders are very few amount; I see, successful traders focus on mainly entry quality rather than session’s name.