I guess that's the only way to make sure you don't get robbed: Research, read what they offer, and find trustable people/businesses.
My opinion (based on what I'm invested in):
NxtVentures is something I like - it's also by a core member, and has already delivered a dividend. This is in the form of shares of other assets - I think it made for a good earnings ratio. They gonna likely pay another dividend in privacyNXT assets soon - so get in before that
After that it'll likely take a month or two again.
Lith (called DORCS in the AE) is cool too. Very ambitious but well planned and it has some core members of the NxtCommunity behind it. Payoff is far away though.
NXTBlocks is a site that's already working for a while. Relatively sure to say that this is no quick scam. They're adding wallets and such. Overall an existing business with huge opportunities should NXT rise. But also quite high risks for the price.
An advantage of those three (of course there are more such assets): They are kinda tied to NXT. Should NXT explode, then the assets will likely too. So you don't lose out.
Also in reverse: Investing in those will help NXT, as it means there are more good services and tools behind it.
Then there are some assets for hedging: If you're not in for NXT directly. Like buying the
Silver Bullion, or even
ShortNXT which trades against the NXT price (reliable so far).
The rest are a bit of a mix - not tied directly to NXT, but still helping the environment:
NXTgen[KHS] and NXTgen[GHS] are mining operations, that worked out well so far. They mine alts and buy NXT which they pay out in weekly dividends. They (and there is another such mining asset) show pics and videos of their facilities and such. So since they buy NXT they support the price.
Naturally there is lots more, but it's getting too many for me to do thorough reading/checking on all of them.
SiaNote for example gets people really excited - and the price is doing well. Maybe worth a look.