I would agree that in domains at the moment the cleanest play is LLLL.coms. Pay the renewals for a few years, (the registry is going to raise renewal prices, anyway), and put them away.
Conventional wisdom is always "buy the best you can afford". My contrary nature says the opposite, in this case. I think as prices rise there will be a shrinking of the percentage difference between the worst and the premiums. LLL.com shows this effect.
But any LLLL.com investment - if bought at good prices - will, in the long term, do very well, in my opinion.