Probably depends on your playstyle. Ground gives you an edge on attack/defense in up to 3 territories. Doing anything else is only to get an overwhelming attack advantage in one battle. I think if you want to magnify the attack advantage in a particular place, then you might consider the advantage of say an artillery piece somewhere rather than infantry, or perhaps even a tank over 2 inf. The only thing that recommends a fighter over the sub is that it is free to move/land somewhere other than just the sea, or for the movement/defense advantage it has in subsequent rounds (this in addition to the extra attack pip at 3 instead of 2) though the sub does have the opening shot to recommend it. If you hit the double deuce you can sink the carrier deck in 37 before normal combat even begins! China is interesting, if letting USA grab a piece of the Bid, it probably makes more sense here than putting the whole bid into sz 11.
I like Egypt for a lot of reasons, so I would probably try to get an infantry unit there at least if nothing else, even if I only had a bid of 3. The difficulty with Russia’s bid battle options is that most of those come down to what the defender is rolling, so there is not a whole lot you can do anyway, other than to put up more fodder to increase the odds on defense from G counter attack. Though its hard to argue against anything that provides a larger stack in W. Russia, or cuts down Germany’s ability to counter attack it. If you go on the ground, its possible to set up a hit on Belo or Baltic with the bid, or to give better odds on a Ukraine strafe, or just to stack W. Russia so deep that G has no shot on it. It is hard to say that one bid is best for every game.
Its not quite like in Revised, where everyone just used the bid for north Africa, or maybe saved a little of that to buy the extra J transport, but in terms of breaking battles, I think the fighter in Egypt is potentially the most damaging, so that’s why I put the focus there. It can do other things besides just the hit on 37 too, it can cover the Med, fly to W. Russia or Caucasus, fly to India etc. Otherwise, as you pointed out, 3 ground is pretty similar whether its 9, 10, or 11 ipcs. Above 9 is optimal, because it gives you the option on a fighter. Whether to actually bid a fighter is another question. Some like an extra Russian fighter, though I think Britain can do more with it.
That said, whether you prefer dice or low luck, may recommend the advantage of one bid over another. I am a dice man at heart, but even 1 extra attack pip in LL could take a battle from a swing to a sure shot. So that might be worth considering too, depending on what style of play you prefer.
Also, its worth pointing out that you have to place your bid before you will know the results of Russia’s opening battles. This can present certain challenges. Say for example, that you bid a sub with the intention of KJF, but Russia gets totally hammered by a German defense. With a fighter you have an option of backing off sz37 and going for something else instead. A sub to attack sz37 also requires that you protect the British fighter in Egypt, (either with the rest of the bid, or with a Russia fighter) which might not be a great option, if Russia got screwed in their opening attack and can’t afford to send a fighter south. That’s why I like the British fighter over the British sub, but it is true, if you spread ground you can accomplish a fair amount with 9 ipcs. 3 ground across 3 territories. 7 or 8 ipcs on the bid is a lot tougher though, since then you can only spread 2 ground across 2 territories.