I don’t think there are any wrong answers to this poll. Each option leads to a common double, but each also has some risks.
The most important consideration is that you absolutely must leave 60 or less after the first dart to give yourself the best chance of having at least one dart at an outer ring double.
Treble 20
Pros: You’ve been throwing at the T20 the whole game, so it’s a comfortable shot. A T20 leaves 2 darts at D4 for the win. A S20 leaves 48, which easily leads to D16 or D20 for the final dart. Even missing into the T5 works – a S13 leaves Tops.
Cons: Miss on either side of the 20 (S1, T1, S5) and you’re looking at a Single to leave Bull or a Treble to leave an outer ring Double. Even if you hit the T20, S4-S2 leaves D1 for your return to the oche. I’m not sure I’m in that much of a hurry to get to The Madhouse.
Treble 16
Pros: T16 leaves 2 darts at D10. S16 leaves 52 which is a Single away from D16 or D20. Missing high into the 8 is fine (S8 leaves 60, T8 leaves 44). Missing low into the T7 leaves 47 which is also a Single away from D16 or D20.
Cons: Missing low into S7 leaves 61 and will require a Treble with the 2nd dart or a Bull finish.
Treble 12
Pros: T12 leaves 2 darts at D16. S12 leaves 56 (S16-D20 or S20-D18). Missing into the 9 is fine (S9 leaves 59, T9 leaves 41). Missing into the T5 leaves S13 for Tops.
Cons: Missing into S5 leaves 63 and needing a Treble with the 2nd dart or a S13 to leave Bull.
I’ve used all of these over the years, but I’m now going the T12 route. I prefer to have my first chance at a double be D16 or D20 and almost all of the outcomes of aiming at T12 with the first dart lead there.
While it does come down to personal preference where to throw the first dart, keep in mind that that choice is also deciding which Double you’ll have to hit to win the game. The last dart is much more important than the first.