There's a few different kinds of Monster in My Pocket collectors: One type collects only Series 1 monsters, another goes after every single toy that was ever made using the Monster in My Pocket name, and then there are some in-between, who collect a few different series. Personally, I consider Series 1-3 to be the "true" Monster in My Pocket series, and though I own some MIMP toys that came later on, I don't actively collect them.
Above is a shot of what I consider to be full set of the main Matchbox MIMP figures, Series 1 through 3, monsters #1 (Great Beast) through #81 (Blemmyea). I'd be wanting to get a photo of all these monsters together for a while, simply 'cause I'm a geek like that. I finally got a chance, and man, all these weirdos together is a beautiful sight. I wanted to include a variety of regular, neon and premium colors to show just how much variety this toy line offered (especially for Series 1).
Looking at them all together, I don't think you can beat Series 1 in terms of sculpting, color variety, and the selection of monsters offered, but I love Series 2 and 3 as well. I only wish the full Series 3 had been released, not just the 9 that ultimately made it out as premiums.
Series 4 continued with the mythological monsters theme, but because of their larger size and painted details, I just never thought they fit in. I still own a set, but I really wish they had continued on in the same size scale and with no paint (some were available unpainted, but not nearly enough to make up an entire set). After that, the line continued with characters like wrestles, dinosaurs, aliens and monster bugs. I consider these to be more of their own toy lines than genuine MIMPs.
What about you? Which series of MIMP do you collect, and which are your favorite? Do you consider later releases to be true MIMP?