I have both the Corsair SP2500 and the Acoustic Energy AEGO M 2.1.
For music, the Acoustic Energy AEGO M 2.1 is clearly better sounding than the Corsair SP2500, but its frequency response on the low-end (the bass), doesn't go as low as the Corsair SP2500.
For gaming and movie, the Corsair SP2500 is better due to the sub can go lower on the bass, thus making it better for effects and explosions sounds. The satellites speakers for the SP2500 doesn't offer as great clarity and details that the Aego M 2.1's pair of satellites speakers for the mids and highs, but it does offer a slight bigger soundstage/environment, mostly thanks to the large drivers in comparison. But do note that the sub of the SP2500 is almost the size of a tiny microwave oven, so you would need to have enough surface area on the floor to place it; whereas the sub of the Aego M 2.1 would take only half the surface area.
So it's really down to between gaming and music which you prioritise more in term of usage. Don't get me wrong, both 2.1 systems are great in my opinion, but they do better than one another in different areas of usage. Also power wise the Corsair SP2500 has the advantage, and can go much louder than the Acoustic Energy AEGO M 2.1; not saying you will use it for this purpose, but the SP2500 can go loud enough even for an outdoor party, whereas the Acoustic Energy AEGO M 2.1 would be restricted to purely in-home use.
As for the Harmon Kardon Sound Sticks III, it is generally seen not as good as the Acoustic Energy AEGO M 2.1 judging by reviews, so I think you probably wouldn't need to consider that.