50i,25p are PAL standards (for those countries that support PAL)
60i,30p are NTSC standards (for the countries that support NTSC) Japan, USA etc
50i and 25p are both 25 frames per second, 50i is interlaced and made up of 50 fields (half frames) per second 1st field odd, 2nd field even
60i and 30p works exactly the same way on 30 frames per second.
24p is more universally accepted, but not a television standard, it is the film standard, and it is digital video adapting to the film standard to avoid having a pulldown, and being able to watch movies in their native frame rate. Traditionally, you WON'T see regular TV shows shot in 24fps.
Get whatever is native to your country. If you are on the PAL system, get the 50i/25p. If you are on NTSC system, get the 60i/30p model.
And the difference between P and I. They say that if all else is equal (including resolution), the P (progressive scan) will appear to be more flicker-free and a higher resolution than Interlaced.