Good investments are all about timing.
The trick to buying a car as an investment is to grab one up in that sweet spot before they become classics and while they're still just considered unremarkable older models. And according to the experts at Total 911, now is the time to grab up a Type 996 911, particularly the 3.4 Carreras. Age is obviously a big part of this, with a couple of newer generations of the 911 having been around for some time, offering as they do more power and better electronic gadgetry, but that's not all of it.
The Type 996 was also the first water-cooled 911, and for collectors of classics, the air-cooled models are just automatically better and they don't hear otherwise. The styling wasn't particularly well liked either, although this is mostly to do with the “fried egg” headlights. The 996 also has a reputation for being unreliable, but this is something which Porsche experts generally find baffling, as numbers will usually put the 964 far in the lead for unreliability. This is therefore probably a rumor started by purists, but it's all good news if you're looking to invest in something that will only go up in value. They've never been cheaper and will only go up in price.