As a rule, you should buy what you like. Watches are not an investment (although many are using this an excuse to buy/sell/trade watches). They are all perceived value. If you're looking to buy and sell in the short term, you don't really need to ask in here what is the best to buy to keep.
When it comes to Speedmaster, you should not go wrong with the standard Moonwatch (I cannot remember the current reference number; too long!) which is sold on either Hesalite or Sapphire. Between the two, my preference would be the Hesalite, which is "truer" to the original Speedmaster which landed on the moon.
With limited editions, Omega (like Panerai before this), tends to drop an LE several times in a year. Not all will carry the same hype, so again, if you're looking to buy an LE Omega, please at least make sure you like it. Because when you can't sell it, hey at least you can wear it.
Just as a reference, in the not too distant past, Omegas never used to resell at the rate they are going for today. Hype and perceived value, demand out weighing supply, that's all it is. Just because the asking rate outside of Malaysia is x value, does not mean that the same watch can sell for the same price here. In Thailand for example, there are fewer Omega enthusiasts (as far as I know). Then there's Singapore, which had one of the highest Ultraman deliveries in the world.