Well, depends on which variant you want

Hasegawa are generally excellent, but be aware that they've actually tooled 2 sets of Phantoms. The older ones (cheaper) are pretty bad, the newer ones are very good, if a bit fiddly.
For Spey engined variants then Fujimi all the way (but good luck finding them under £20). The other Fujimi kits are not as good, but still not bad.
For F-4F and RF-4E then the new tool Revell kits are the way to go. But beware a nasty old F in a Revell box - raised panel lines, atrocious fit!