There are two separate issues here -- which airline to fly, and which airline to credit miles to.
ANA: better food, better service, don't like the seats.
UA: if you take the 747 ex-LAX you get the new business class seats which I find much better for sleeping (fully flat, not angled-flat) but of course you get UA service and UA food.
Either way 10-12 business class roundtrips will make you a United 1K if crediting miles to Mileage Plus. 1Ks get 6 'systemwide upgrades' per year which will get you from business to first class, confirmed at booking (subject to availability) or from coach to business from most fares except the very cheapest. In addition you should earn 8 confirmed domestic upgrades plus other 1K perks.
Now, if you fly United and credit to United and you're paying for 10-12 transpacs a year you probably make Global Services. Search the United forum for discussion, but priority on most things is above 1K.
The downside to crediting to United is, as noted above, 'Starnet blocking'. United is the only Star Alliance airline that doesn't actually let you book all award seats being offered by Star Alliance partner airlines. They 'block' various partners on various routes on various dates in a very non-transparent way. So for redemptions you pretty much want to stay away from United.
Are elite benefits more or less important to you than mileage redemptions?
I should also note that programs like bmi and Lufthansa Miles & More are more generous with mileage earning on premium class fares. Seriously consider (a) asking bmi for a status match and then (b) crediting to bmi. While flying the airline which appeals more to you -- United's hard product on the 747 or ANA's better soft product?
Of course if you're otherwise looking at the United 777 out of SFO or SEA, those haven't been upgradeed yet, you DEFINITELY want to stay away from those in business class, ANA is a no-brainer from SFO hands down...