Currently, I am trading with IG, Oanda and Coinexx. IG and Oanda are regulated brokers and Coinexx is not. I like to diversify my funds so I always trade with 3-4 brokers at a time.
I think one can get a fair idea about spreads and prices using demo accounts. And that is how I always go when I have to choose a broker. But for better understanding you can simply compare their demo spread with the live account, if it does not match then you can think about clarifying it.
That’s a good and safe approach.
it is my main broker, it has good servces