The LED Sonic torch is very small and doesn't extend or produce sound. It also doen't have any paint details and is pretty cheap looking.
The Sonics included with the Vortex Manipulator and the Journal of Impossible things are a touch larger and sport a superior paint job with additional details in the sculpt, but it is still quite smaller than the one on the show. They also do not extend.
The first generation Sonic with the UV LED and the note pad has a very odd sort of cream color on the handle and has a few new and improved paint details. It's larger than the screen used props, but does extend and have two screen accurate sounds.
The second generation Sonic with the UV LED and the Psychic Paper has a more accurate paint job and is very nice. The UV LED shines purple instead of bright blue, though, but the Sonic Paper is pretty much perfect. The Sonic also extends and has perfect sound.
The Soinc included with the Sonic Pen is the best. It is the same size as the UV versions, which is a bit larger than the one on the show. The paint job has been refined and a few small problems on the second generation UV has been fixed (blotches, a few paint smears on mine). The LED is the perfect shade of blue and shines bright, and the sounds are again perfect (though I suppose a little quiet, but I personally don't want it to be ear-splitting). The pen has a very bright LED and the same sounds, just like the show, and it writes well. I don't like that it is so oversized... it's almost novelty-sized, but would look good on display.
So yeah, I agree the one with the pen is the best, with the second generation UV LED Sonic with the Psychic paper coming in second.