Well, I can try to answer that - with the big caveat that I haven't actually examined either kit in at least 35 years. But I built both of them several times, and my old memory is fairly about stuff like that. (Don't bother asking me about something that happened the day before yesterday.)
The Revell kit is a little older and quite a bit smaller. The latter is an important factor when it comes to rigging. Revell's upper spars are really, really skinny; it's tough to rig them without pulling them out of alignment. It has a great deal of molded detail - including wood grain, which some people like and some people hate. The planking seams on the hull are countersunk - including the 5-sided "anchor stock" planks on the wales. (None of the wood kits - even the big, excellent one from Jotika - shows that detail.) The guns on the upper deck (the first one down from the weather decks) have individual barrels; their carriages are molded in with the deck. (The only way to see them is to look carefully under the gangways. Most of the gunports on the lower and middle decks are molded shut. A handful of them, amidships, are open; the guns themselves are individual parts with integrally-molded carriages that sit on little shelves molded in with the hull halves.
The Airfix kit is a little newer and significantly bigger. That makes for sturdier spars. All of its gunports are molded open, with separate lids. The guns in the waist on the upper deck (between the quarterdeck and the forecastle) have individual barrels and carriages - but only in the waist area. Fore and aft of that area there are no gun carriages.
The guns on the middle and lower decks, and the upper deck toward the bow and stern, are "dummies" - stub barrels glued into holes in shallow, depressed squares where the gunports go. Personally, I don't like that feature. If I were building the kit again (heaven forbid), I'd probably glue all the portlids shut. (That's a perfectly valid way to represent a ship of the line. Longridge's famous model, the subject of his book, The Anatomy of Nelson's Ships, is built that way.)
To my eye there's something not quite right about the Airfix kit's bow. The knee of the head doesn't stick up high enough, with the result that the gap between the figurehead is too big. I'm not quite sure where the problem is, but to my eye it's pretty prominent. Other Forum members haven't thought so.
The molding of the intricate system of bow rails is better in the Airfix kit. The Airfix version also scores in having separate bulkheads under the break of the poop deck. (The Revell one is "cleared for action," with those bulkheads missing.) The Airfix one has nicely done stanchions supporting the beams in the waist; the Revell one doesn't.
The detailing of the carvings on the bow and stern are good on both kits - though the glass in the windows is represented by solid plastic. Since the Airfix one is on a slightly larger scale, the carvings on the stern are a little bigger (and easier to paint). And Airfix's figurehead is beautiful.
Both kits have "copper sheathing" that looks pretty reasonable for the scale. The Airfix version doesn't have "wood grain." Most of the hull planks have countersunk edges, but the edges of the "anchor stock" planks on the wales are represented by raised lines. Kind of odd-looking.
Both kits were originally released with plastic-coated thread "shrouds and ratlines," which I think were utterly awful. Recent issues of the Revell version use injection-molded plastic parts that are even worse. The Airfix kit now comes with a "rigging loom," which frankly I regard as silly. If I were building either kit I'd rig my own shrouds and ratlines.
Either of these kits can be turned into a good, serious scale model.
That's about the extent of my memory. Hope it helps at least a little.