I use whatever ATC call me.
That* is what I was taught in BE, too.
When changing frequency, carefully note what the other party calls you. For example I could depart my homefield and call "xxx traffic, OO-G86 leaving the circuit and the frequency, expect back in two hours, OO-G86", then switch to Brussels info "Brussels Indo, from the Oscar Oscar Golf eight six" and they might reply "Oscar eight six, Brussels Info" and I was O86 for the rest of the conversation.
Note that on your homefield it may matter little, most other pilots will know you anyway and you will know most of them, including the sound of voice, the difference in voice when annoyed or amused, and also the type of plane and its typical usage. For example, when at my homefield I heard Whiskey-8-3** calling, I knew it was the ultralight that the club used for elementary training.
* with the detail note that it is not limited to ATC, it applies to any ground station, be it Control or Info or Tower or whatever.
** identity changed for reasons of privacy