I was wondering what format of the game would have the best results. Is it better to use the actual disc in your DVD rom, or to create an image and run it from your PC either directly or using DAEMON tools?
Technically there is no difference, the game will still behave in the same way.
On other emulators such as PCSX / ePSXe / PSXeven / Gens (SEGA CD) it would offer a speed up in game play as data read times are faster from a HD compared to a CD / DVD drive, also this had the effect of reducing 'pauses' as data / audio etc are read.
With PCSX2 this has no effect, as physical emulation of the CPU's, graphics etc are slow already, to put it simply the game is running so slowly anyhow it will not out-pace the disc drive, also the % of CPU time spent with VU emulation etc means that even with the theoretical speed up, you're talking fractions on an FPS count.
Both will yield the same results. There is no difference right now as far as one working better than the other. Later on, (when things are faster) ISO will be the ideal way to go, since a hard drive can be read much quicker than a dvd, but for now, there's nothing to be gained.