I used to use ICmarkets thinking that there were a A Book broker but I have started trading with VARIANSE which has excellent trade execution and raw spreads, I think they are a A Book broker
I guess all brokers resort to matching your orders with other clients, i.e. act as an execution venue, when position size is too small to pass it to the liquidity provider. So there is little need to care about that if your trading returns are not so high to cause pain to your broker.
You can have a look at turnkey forex, trader’s way, and fxchoice, their spreads mostly remain low, especially for major currency pairs.
The brokers with the lowest spreads, in my opinion, are CMC and FP Markets. Their spreads average 0.1 to 0.3 pips for most parts of my trades.
Currently, I use FP Markets because the spreads are stable even during volatile market conditions.