3 to a royal or 4 to a flush?
Keep the three to a royal. Exact EVs on 9/6 Jacks or Better: Q-J-10 suited is worth 1.4792 per coin vs 1.2766 for the four-card flush draw — the royal's 800-coin jackpot outweighs the extra flush outs.
The exact numbers — Q♠ J♠ 10♠ 7♠ 3♦
EVs are exact — every possible draw enumerated, not simulated — at max bet on 9/6 Jacks or Better. Check it yourself: the analyzer runs the same solver in your browser.
See all 32 holds of this hand ranked →Why
The four-flush completes more often, but everything it makes pays 6. The three-card royal keeps the 800-coin jackpot alive AND still makes plenty of flushes, straights, and high pairs along the way. High royal draws are the great exception to 'more cards to the draw is better' — the jackpot equity dominates.
Chart line #7 of 18 (3 to a royal) sits directly above line #8 (4 to a flush) — this hand is exactly why that ordering matters. See the full solver-optimized strategy chart, or drill hands with exact-EV feedback until plays like this are automatic.