Hi and welcome to the forum. The problem, as you have already discovered, is that there are way too many options!
Some of the questions that might need need to consider first are:
- Do you have any airlines you DON'T want to travel with?
- Do you have Frequent Flyer Miles to redeem / do you want to collect FFMs?
- Have you looked at the RTWs oferred by all of the alliances? If you check OneWorld/Star/etc, they should have quotation pages.
- If the trip is going to be over an extended period (say 8 weeks) then connections and through ticketing is of less importance
- Are you staying with friends/family, or do you think that some of the alliances might have deals on hotels etc.?
- With regards to Premium Economy (of which I am a great fan) when you have a short list of carriers, check their web sites to see if they have a PE option, most do not. However, the alliance sites with their 'book an RTW with us' normally only offer Y, C, F classes - even though some of their carriers have PE. So, again, you have to cast your net wide at this stage.
- For the long Pacific sector, if you cannot find a carrier with PE (consider NZ from AKL to SFO or LAX) I would suggest EITHER breaking the journey in HNL or simply paying for Biz.
Apart from the Alliances - which DO have many advantages - take soundings from the usual suspects of web sites as you might find the routing you want - even if not the price! I like this (US centric)
Hipmunk: Better Flight and Hotel Search as a way to find routings that are direct (without tech stop) or more interesting (with tech stop!).
Lastly, with the Alliances, perhaps visit each and note which carriers they have (big and small) and see how these match up with the ones that have PE? Yes, it's a lot of work to research but can be fun!