I have experience a lot from trading in the short time that I have being trading and for sure, I is far better to trade a single coin than multiple coins, just as I mentioned in my earlier comment on the risk of trading multiple coins and my bad experience from such action.
My reason is that, I with a single coin, pier you can make a clear analysis and also build the basic concept and tool to always be on a profit side all the time or minimise losses.
For new traders, I think BTCUSD is the only pair they should focus on and trade to gain experience. BTCUSD has all the conditions of a reasonable trading pair: well-known, large trading volume, large number of traders participating, and less manipulation.
However, more experienced traders will seek out many trading pairs to take advantage of capital, opportunities, and time in the market to generate maximum profits. As I see it, they often trade other pairs like ETHUSD, DOGEUSD, BNBUSD, SOLUSD... and also make a lot of profit!"