Bits : thin o-r thick ? :Bits?

I'm really sorry, but I only use Snaffle bits. A circle ring snaffle. My horse kinda pulls a little in excitement, so I use a semi-thin, to medium thickness to keep her under control. i have very soft hands with her too, but that bit works the best for us. she always had tom thumb bit but she always put up a fight because it was too uncomfortable and way too thin