If you've followed this blog for any length of time, you'll have noticed that I've never been very consistent in the way I present monsters. That's because I'm constantly experimenting with different formats and I haven't yet managed to find a perfect one -- "perfect" being that combination of exhaustive yet succinct that quickly gives me everything I need to know when using a monster in a game.
When I was a kid, I was very fond of the AD&D Monster Manual presentation, but, as I get older, I find I like it less. I feel it gives too much information to be useful in play. As a reference, it has value, particularly if you're of the Gygaxian naturalist persuasion. I myself have definite sympathies for that approach, but there is, I think, a danger in the way that the extensive Monster Manual descriptions, especially those of the 2e era, set details in stone and implicitly establish an "official" interpretation of a creature. The "Ecology of ..." series is the natural evolution of this style of presentation and not one I much admire these days. For my money, the Moldvay/Cook presentation of monsters comes closest to perfect, although it has a few flaws. The biggest is that it doesn't include "% in Lair," which is essential in a sandbox campaign or indeed in dealing with randomly-rolled wilderness encounters. I also think the inclusion of the XP value of each monster would make these entries more immediately useful.
Of course, in the end, the form of the monster listings themselves is less important than the short form used in modules. Nowadays, the term for this is a "stat block" and, if I had to point to a single thing that drove me screaming away from 3e, it was the ridiculous lengths of its stat blocks. In the old days, most modules used a very abbreviated listing for monster statistics, with the inclusion of individual hit points being the only constant. I think that's probably too little information unless you're running a LBB-only OD&D game, which is why, again, I prefer the Moldvay/Cook short form for most of my purposes. It's very usable, sacrificing neither speed nor clarity, and, most importantly, it doesn't take up half a page even when describing extremely powerful creatures -- a huge improvement over the WotC editions.
I'm going to be posting some sword-and-planet monsters over the next few days and I'll likely be using my latest ideas about the "perfect" presentation of monsters for old school D&D. Like everything here, I'm always open to suggestions on how to refine my raw ideas. As much as the monsters themselves, I'll be looking for thoughts on their presentation, since I'd like to come up with a consistent way to present them that I can use from now on.