I tend to make offerings and perform rituals to all of them at once (unless it's Lughnassad or similar, when I concentrate on the deity being honoured on that day), so I usually get equal amounts of time with all of them.
And to answer your question about knowing Who did What, I return to my example about the decision. It was easy to tell then, because Manannan pretty much straight-up told me that he was sick of my whining, so he was going to lend me to Aenghus for the week so I could sort it out. It was fairly easy to tell who had their hands in that particular piece of work

.
But at other times, I've certainly asked who helped me at one point and Manannan, Aenghus and Lugh have
all given me the metaphorical innocent eyes and a "Who, me?"
Fairly sure it was one of them, they're not telling who. Guess I just live with that, puny mortal that I am.

Hope that was in some small way helpful.
It is helpful... I have trouble focusing my energy on just one, at the moment. Hermes will always be paramount in my affections and attentions, but at the same time, I don't want to offend either of the goddesses I have taken up. I'd like to develop an "equal" relationship with all three, but maybe that isn't possible... much like with (as folks here have stated) friends. Not every friend is going to be a person's favorite.
I, also am doing offerings for all three at the same time, and am trying to 'talk' to them at the same ritual/prayer/sitting.
As for your "Who, me?" moments... not only did that make me laugh, I think it's likely from at least ONE of my three deities. Heheh.
I have considered taking a single day at some point in the future just to focus on one of the three... and I wonder if anyone else has done so?