Q was so integral to the Star Trek: The Next Generation series that a TNG collection is incomplete without him. Playmates released only two Q figures (as far as I know): one in Starfleet uniform, and the other in his judge's robes. (EDIT: This isn't exactly true; see comments below.) Fortunately, I didn't have to choose, as I won an eBay auction that included both figures. But which one is the must-have Q for a Playmates Trek collection?
Stats
Year Stamped: 1993 (Starfleet uniform Q), 1994 (judge's robes Q)
Company: Playmates
Size: 4 1/2"
Price: $4 for both, loose from eBay
Packaging: Carded
Looks: Starfleet Q
Judge's Robes Q 
The first Q wears the Starfleet uniform that he frequently donned in episodes like True-Q. The sculpt is an effective likeness of John de Lancie, with that Playmates caricatured style that is so much fun. And thankfully the body sculpt is unique (at least, from what I can tell), despite the fact that there were plenty of Starfleet uniformed bodies at the time from which to reuse parts. He also has a good height to him, which is appropriate given the fact that de Lancie is a tall drink of water himself. The right hand is sculpted in the gesture that Q uses when he conjures something up, which is a nice touch.
The second Q released is clothed in the judge's robes from Encounter at Farpoint and All Good Things. The figure matches the costume from those episodes pretty well, and the likeness is another great Playmates caricature. But like many robed figures from this time period, this Q suffers from Salt Shaker Syndrome: the robes are sculpted in such a manner that they force the figure into the shape of a salt shaker. Also, the body of the robe has a slightly darker hue than the sleeves. I'm not sure if that's because the plastic is discolored by age or if it was always a different hue, but it's distracting nonetheless. He's also not quite as tall as Starfleet Q.
Articulation: Starfleet Q
Judge's Robes Q 
Starfleet Q has the usual Playmates Trek articulation: swivel neck, swivel shoulders, hinge elbows, swivel waist, swivel hips, and hinge knees. I suppose you could consider this "hyper-articulation" for the early 90's. The only problem is that the cut of the hips is such that it forces the legs to spread wide when he sits. Sure, that's great if he's stretching for Worf's calisthenics, but it's horrible for sitting on the Enterprise bridge.
Judge's Robes Q has articulation typical of robed figures from this time period: swivel neck, shoulders, wrists, and hips. Not only is that a comparatively low number of POAs, but the robes that force him into his salt-shaker shape make his hip articulation effectively useless. He certainly can't sit on his throne, which is pretty much all he does in the series when he's in this costume. FAIL.
Accessories: Starfleet Q
Judge's Robes Q 
Starfleet Q comes with the usual TNG insignia stand and a dilithium crystal, for some weird reason. (A side note: I've seen a carded Starfleet Q with a red crystal instead of a purple one. The crystal above might be from another figure, but it's the same sculpt anyway.) He also comes with a mini Earth and a micro Enterprise that might be the coolest accessories in the entire vintage Playmates Trek line. You can pretend that Q has increased his size to planetary proportions to torment humanity and the Enterprise crew. The Enterprise isn't particularly detailed (especially compared with the Galoob Micro Machines Enterprise) but it's a great pack-in anyway.
Judge's Robes Q comes with a more specific Q Continuum stand, which I really dig. He also comes with the lion statue that sits next to his throne. The statue looks pretty cool, but he only seems to come with one while in the series there were two (one on either side of his throne). Q's accessories are rounded out with his judge's gavel, signature sceptre (the same as the first Q), and a scroll (which didn't come with this sample). The accessories are appropriate but most decidedly boring. I would have much preferred him to come with a throne, but in order for that to happen, he would have to be able to sit first. :/
One other thing, they both come with cards: Starfleet Q with a collectible card, and Judge's Robes Q with a Pog card (later releases of Starfleet Q also came with a Pog). Pogs were after my time so I have no nostalgic reference for them, but if you're a milk cap fan, you might dig it.
Value:
At only two bucks a figure, you can't go wrong with the price. Although it used to pain me to see my beloved Star Trek figures plummet in value so dramatically, I'm not so distraught when I'm buying them.
Coolness: Starfleet Q
Judge's Robes Q Starfleet Q is a cool figure with a cartoony, toylike sculpt and accessories that are all sorts of awesome. But the Starfleet uniform isn't particularly distinctive since there are many figures in the toy line with that same costume. Maybe it would have been cooler for the figure's costume to come from Deja Q (the episode in which he became human). I admit the Starfleet Captain's uniform is the costume in which he's most often seen in the series, so it's appropriate for the character.... it's just that this Q isn't going to pop on the shelf.
Salt shakers aren't all that cool, so Judge's Robes Q can't expect to score well in this category. Not being able to sit really hurts the figure. Even though he doesn't come with a throne, you can't even make a custom throne because it would be pointless to do so. Still, unlike Starfleet Q, the judge's robes costume is distinctive and specific to the character.
Overall: Starfleet Q
Judge's Robes Q Starfleet Q is the clear winner of the Battle of the Q's. His face sculpt is a fun caricatured likeness of the actor, his body is appropriately proportioned with effective articulation, and his accessories rock lobster. Judge's Robes Q is the big loser this time. He certainly looks distinctive, but his robes force his body into that annoying salt shaker shape that effectively destroys not only his articulation, but also any sort of fun you can have with the figure. If you're a big Q fan, you'll likely want to buy both because they depict totally different costumes (and they're cheap). But only Starfleet Q is truly worthy of being in your collection.
