900 Mhz :
Pros – Brilliant range, great penetration
Cons – Illegal for use in the UK, band used by mobile phones
1.2 Ghz :
Pros – Great range, good penetration
Cons – Illegal for use in the UK, band used by other sources
1.3 Ghz :
Pros – Good range, good penetration, very clear band
Cons – Not legal for airborne use in the Uk
2.4 Ghz :
Pros – Good range, cheap equipment price, lots of none FPV equipment on the 2.4ghz band can be used with FPV equipment such as antennas
Cons – Bad penetration properties, band used by other flyer’s, wifi equipment, bluetooth etc.
5.8 Ghz :
Pros – Good range, cheap equipment price, band very clean due to low amount of other users. with circular polarized antennas no loss in reception quality.
Cons – Very poor penetration
(Picked from the web, not my own text)