These are the grinding strategies that I shall recommend.
USA:
Purchse F-4S Phantom II.
Germany:
Purchse Tornado IDS WTD61.
Soviet Union:
As of now, there is no easy way. If you have Su-7BMK, or will wait for a sale, go for Su-7BMK, and then Su-17M2. Otherwise, you can purchase Be-6 and grind for Il-28Sh, then Su-7BKL, and then Su-17M2 as aforementioned.
The reason for Il-28Sh over Il-28 and Su-7BKL over Su-7B is the slightly higher RP efficiency.
UK:
Purchase F-4J (UK) Phantom II.
Japan:
Purchase F-4EJ ADTW.
China:
Purchase A-5C, and then grind Q-5L. Please do not consider J-7D as an option, not even for an air-to-air grinding path, as long as it has the same BR as J-7E. Even for air-to-air combat, A-5C is better.
Italy:
Purchase F-104S TAF.
France:
If you have Milan, or will wait for a sale, go for Milan, and then any T7 aircraft for bombing. Otherwise, purchase Mirage F1C-200.
Sweden:
Purchase Saab J35XS. Note that you will use a full load of rockets to bomb the bombing target.
Israel:
Purchase Kfir Canard.