I have mentioned loungebuddy on here a few times before – a great little app of which I am very fond (note I have no connection with loungebuddy other than as a user and an occasional, unpaid, contributor)
Recently I stumbled across their guides to the three alliances – and if you scroll down to the table of benefits the differences are quite significant. Here are the links:
IMHO oneworld benefits are the best – not only because they have three tiers, but also because the second-tier benefits are quite significant, including lounge access. Top-tier members get certain additional benefits (first class check-in and lounges, and fast track at some of the world’s busiest airports).
Star seems to me the worst, since second-tier members get nothing very much, and first-tier benefits do not include access to first class lounges, nor do they offer anything that isn’t available to top-tier members in the other alliances.
SkyTeam seem to be somewhere in the middle of the two, with no lounge access for second-tier members and no first-class services, but a useful ability (for the business traveller who can’t always plan far ahead) of guaranteed seats even on sold-out flights.
Of course, people’s priorities are very different. However, it seems to me that for the frequent traveller who often flies business class, oneworld gives access to certain first-class treatment which would genuinely improve their experience. For the business traveller who needs trips at short notice on busy routes, SkyTeam offers a clear advantage. I suppose Star’s strength is the size of its network, but I don’t see much else to distinguish it from the other two.