High pair or 4 to an outside straight?
Keep the high pair — it isn't close. Exact EVs: jacks are worth 1.5365 per coin; the open-ended 9-10-J-Q draw only 0.7872. Breaking the pair costs nearly half its value.
The exact numbers — J♣ J♦ 10♥ 9♠ Q♣
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
A guaranteed 1-coin return plus improvement chances crushes a 4-coin straight that hits about 17% of the time. If the flush version of this question is 'clearly keep the pair', the straight version is 'don't even think about it'.
Chart line #6 of 18 (high pair) vs #10 (4 to an outside straight). See the full solver-optimized strategy chart, or drill hands with exact-EV feedback until plays like this are automatic.