Semtex has a slightly larger blast radius of a frag nade, can stick to people and takes less time to detonate then an uncooked frag nade.
Frag nades however have the ability to be cooked, travel much further due to longer det time and can roll which is sometimes useful.
However C4 is better then them all because it's just so much funnier. Although you lose a ton of range it doesn't show an icon on the hud like a nade will and can be detonated whenever you wish, but can be blown up or rendered temporarily useless from flash/stuns (which is stupid).
Frag nades however have the ability to be cooked, travel much further due to longer det time and can roll which is sometimes useful.
However C4 is better then them all because it's just so much funnier. Although you lose a ton of range it doesn't show an icon on the hud like a nade will and can be detonated whenever you wish, but can be blown up or rendered temporarily useless from flash/stuns (which is stupid).