For those who have miles with United, what's the most economical way to use?

One way to SE Asia costs 40K in Economy or 80K in Business (Polaris!!). Depending on where you are going and where you are originating from, this is a good use. Also kind of depends on the cash value of the ticket since this will assign a "value" to your points. If you are getting anything over 1.7c per united mile, you should do it. (Cost of cheapest revenue ticket mins award tax and fees, the $81 divided by 80K). Personally, I would consider anything above 1.4c as long as I don't have to use cash.

Remember - one benefit of using United miles is that you can book a stopover for free. So say you are flying Asiana into Korea, you could stay there a week then go on to another country for another week, then back. Stopovers can be a year long but have to be in the same region.

Another benefit is to use open-jaws. 2 open jaws are allowed by United. So you could fly into Incheon (Destination) for a week, catch a cheap flight to KUL on a budget carrier, spend a week there (open jaw), then continue on to Bali, stopover, spend a week, then fly back to the US (which doesn't have to be your origin). All this on 1 united award + 1 one way on a budget carrier.

Just remember - Open jaws and Stopovers are only allowed on RTs and you have to originate and end in the same region (aka USA). Stopovers and open-jaws are permitted within the same region.

One last thing - good luck piecing together a complicated itinerary with the UA devaluation last year. Basically, if you can't see a route on the website, it will not be bookable within the same ticket. You HAVE to be able to build it yourself online.

The only real benefit of Silver is that you get access to a little more award space on domestic United flights, and option to pick Premium Economy for free on domestics. Is that valuable to you? Only you can answer that depending on your flying habits.

Star alliance is huge and the best way to get to Asia. You have Asiana, Singapore, EVA, Thai and United that fly into Asia.

So in summary - the "best way" to use UA miles is to get at least 1.5c per point and add in a stopover and open jaws in international itineraries.

If you say exactly where you want to go, I can give you some advice as to how to go about doing this. 135K will get you anywhere in the world in Economy.

I just remembered Japan is a region of its own and not a part of "North Asia." Therefore, you cannot do a stopover within the same ticket if you want to visit those two countries. Pretty stupid. All other Airlines define North Asia or Asia 1 with Japan included.

Anyway, you could do RT in business for 145K UA miles total. 65K from LAX to KIX via SFO on United Polaris, and 80K on the way back on Asiana/Air China. Availability is wide open.

You could do the same trip in economy. RT for 70K UA miles plus some change in fuel surcharges. Buy a cheap ticket between Japan and South Korea as CuseTiger suggested.

You could also do one way in First for 110K and back in Economy for 35K. Or any other combination that you want.

ETA: I priced out your itinerary on google flights and it looks like the price is $914. Subtracting fees on the award $45 and the connecting flight KIX-ICN $77, it looks like you would be getting 1.1 cent per mile value booking an economy ticket. Rather poor "value" if you ask me. Plus no redeemable or elite miles. This is more often than not the case with flying economy to asia. Prices are too damn cheap.
If you can, I'd buy this ticket with cash and save the miles for a more aspirational award. That said, miles devalue often, so unless you have travel plans in the next year or so, I wouldn't sit on the miles for too long either. if that is the case, I would fly the outbound on United business on the brand new Polaris product. 65K there in biz, 35K back in economy = 100K.

ETA 2: Remember, that the PQD (premier qualifying dollar) requirement is in addition to the PQM (premier qualifying miles, or actual flown miles) or PQS requirement. You need to fly at least 25K in paid economy flights, plus spend $3K to hit this threshold.

I flew Asiana across the Pacific in Biz on the way to Bangkok on points a year ago. It was the tits.