Joker and nothing else — what do you keep with it?
Keep the joker with a middle card. On 20/7/5 Joker Wild W + 7♦ is worth 1.4841 per coin vs 1.4313 for the joker alone and 1.4000 for W + the queen.
The exact numbers — Joker 2♣ 7♦ 9♥ Q♠
EVs are exact — every possible draw enumerated, not simulated — at max bet on 20/7/5 Joker Wild. Check it yourself: the analyzer runs the same solver in your browser.
See all 32 holds of this hand ranked →Why
Kings or Better is the whole explanation. The queen pays nothing as a pair here, so W + Q♠ is worth less than throwing the queen away and keeping the joker by itself. A middle card beats it because rank 7 sits inside five different straights and the queen inside three, and with the joker already filling one slot of every straight, that is where the extra value is. Note how small the whole question is: every hold worth considering here lands within 0.1133 of the best one, and the chart deliberately merges 5 through 10 into one line — the 0.0230 between the 7 and the 9 is finer than the chart resolves. The joker alone is still worth 1.43, more than most four-card holds without it.
Chart line #16 of 35 — 'W + one middle card (5, 6, 7, 8, 9 or 10)' — the second-to-last line of the joker half, sitting just above line #17, 'the joker alone — draw four'. See the full solver-optimized strategy chart, or drill hands with exact-EV feedback until plays like this are automatic.