Really depends on what your goal is and how the game unfolds. But here is what I like:
Germany - Lots of ground units, a few planes and a 30-ish TUV of ships (CV, DD + TRS). My recent experiment with the DS strategy adds a bomber-heavy build to that as a strong alternative.
USSR - Like Nippon, I like to go heavy on INF and ART/MECHs, depending on what I try to accomplish. With ART, I calculate how many of them will increase the number of Russian surviving units after a counterattack. If you build too many, you will see a faster decline in the number of surviving units than the decline in total number of attacking Russians. With MECHs, you can in some cases even hold Belarus, but against Sea Lion they are a must.
Japan - J1 2TRS + 1IC or 3TRS. If you know JF is coming from the USA, I’d go for the IC, otherwise a 3rd TRS. After that it depends. If you can stay ‘in control’ of SZ6 as a set up piont, add Carriers for the aircraft to land on. FTR, DD, SUB and MECH are all very much needed, but depending on the situation, one may be needed more than the other. If the USA is not pressing Japan a lot, add another IC in Asia and build up to 6 INF/MECH per turn.
US - CV, FTR (to give each CV 2 air at least), SUB, DD, TRS, load (for the TRS)
China - tech rolls indeed seems a good one to me :lol:.
London - FTR, MECH, INF, ART, ARM, IC, CV, DD, SUB, STR…
India - mix of INF + MECH and if it looks like they will survive, an occasional FTR. Even 1TRS is an option if Japan has nothing in range to deal with it (not very likely).
Italy - air and MECH. The odd ARM. Once Italy has >20IPCs per turn I like to squeeze in a ship or 2 (or 3) per turn as well.
Anzac - defensive builds: FTR + INF + the occasional TRS. the FTR can land on US carriers once the allies start to take offensive actions (or sooner, if Sydney is safe). The strong part of air is that they are great defenders and are not as difficult to activate offensively later on.
Offensive builds: FTR, TRS, INF, ART, SUB, CV.
France - … Once Paris is liberated, INF to start with, ART later on.