The only thing that I know is your chances of winning will grow if you open with a 2. Spending your low cards will make your hand stronger. You can calculate your chances by assuming your opponent(s) will always play a winning card. The more they spend their winners, the weaker they become. Or you can calculate from a suit of 1 card (no winners) to a suit of two cards (again no winners) to a suit of three cards (a tie or a winner). At a suit of 4 it becomes more complicated but a tie is very likely. There is always the possibility (especially in even numbered suits) of a tie (if everyone keeps playing the same cards). A sure way of trying to lose would be to always play your second to highest card.
But if I know you're opening with a 2, wouldn't I just lead a 2 as well? There is no best first card, actually. As long as you're following a strategy which I can anticipate any part of, I'm at an advantage over you. In this case, the advantage is slight, since I can make your 2 worth a contested point you might want to throw a high card on, instead of just a point to me which took a 10 or something. It's definitely useful to think about the different length suits. As you get to 4 cards, you get into Level 3 Yomi- there's a best card you want to play (4) and I have a counter (1) but you have the counter to my counter (2) and I have the counter to that (3) which is countered by your original best play (4). The 3 is third level yomi, and the fourth is loop around of first level yomi. It's the beginning of true strategiery! (Note:Made up/nonsense word for strategy.)