Here are my top five.
1. Mecha Clones (Bioman) - In episode 1 alone, not only did they kill civilians, they bloodied them up. Still, it was fun seeing them explode whenever a Bioman hits them.
2. Anaroids (Dekaranger) - Even though they're considerably weak compared to other foot soldiers, I love the fact that they're portable and they played a great part in showing how much of a badass Deka Master is.
3. Nanashi (Shinkenger) - With Shinkenger, no longer were the bad guys limited to skinny foot soldiers, as the Nanashi wear considerable amounts of armor. And they're probably the most intimidating in looks. The drawback is that they are very stupid, as seen in The Decisive Battle movie where the Shinkengers poorly disguise themselves as Nanashi units.
4. Gormin (Gokaiger) - Unlike most foot soldiers, these guys actually have personalities. They react to stuff like normal people (ex. in episode 1, one Gormin is pointing at the garbage truck created by the Goranger Hurricane) and play cards on their free time. But just like the Nanashi, they are very stupid, as observed in episode 10 where Joe and Luka-chan put on gray buckets while infiltrating the green Zangyack ship.
5. Jimmers (Liveman) - These are foot soldiers that can actually put up a fight. Chop off an arm, and the arm will still jump and strangle you. You'll really need to destroy them piece by piece to get the job done.
Honorable Mention: Kunekune (Megaranger) - Their twisted faces give them a lot of character. And the ability of thousands of them to form a giant monster is phenomenal.