I have a Ritter Photon Freedom in one PSK.

A Princeton Tec Pulsar II in one PSK.

A Variety of cheap pushbutton Keychain LEDs in different PSKs and FAKs.

A MagLite Solitaire in one PSK

A MagLite 2AA with Night-Ize LED kit in my Large FAK.

And I EDC a Pelican M6 2330 (too big for a PSK) and an ARC-AAA Premium on my EDC keychain PSK.

Out of all of the PSK sized lights, my favorites are the ARC-AAA and the Ritter Photon. However, I have to admit that the Arc-AAA has the upper hand due to durability, it's waterproof up to 100', brightness, and battery. Really the only drawback for the Photon, and this is purely personal opinion, is that the clip for the Photon Freedom is an odd shape to pack in my hardcase PSKs (Otterbox 1000, Witz Keep-it-clear) and so often gets clipped to a lanyard on outside with my whistle.