I invested in curecoin and then found out about gridcoin. Both are "help the medical world" coins. Which one has better LONG term prospects and why? Are there other coins in this sphere?
To me it's a bit of Apple vs Microsoft in the early days (although it's more Apples to Oranges). Both coins face similar challenges in terms of centralization (reliance of work units coming from Folding@Home or the BOINC networks).
Even though Gridcoin was able to decentralize it's coin (BTW no currency is truly decentralized, but that's another discussion), the transition came at a price of some exploits, and some user's lost coins along the way. The last Gridcoin reboot didn't seem to catapult it's true value inside the crypto community bubble.
CureCoin has faced its challenges with missed ETAs on CureCoin 2.0 (which will be decentralized) But has been stable through its two year history. Their plans are ambitious (esp. with SigmaX) but resources are limited. Even if CureCoin released 2.0 today, it's value would likely come from outside the current bitcoin community (that's just my opinion). The true value for crypto purists would be in the SigmaX PoW.
Speaking of the broader crypto community, they continue to fixate on things like Litecoin, Dogecoin "To The Moon" :-D, and most recently Ethereum's Frontier is sucking up a LOT of GPU power. Some suggest science coins could create Ethereum tokens, which would be cool, but then it would just be an Ethereum version of FoldingCoin - which already lives on CounterParty, and derives it's value through donations distributed to protein folders.
The polarization between long-time distributed computing participants (anonymous altruists) and typical bitcoin investors (ethical egoist) could NOT be more opposed, and perhaps this is another challenge all science coins face. The loudest voices on bitcointalk tend to whip things into a schizophrenic frenzy in order to benefit themselves. This is truly unfortunate.
Some parting thoughts:
GridCoin has a large community with a diverse mix of projects, but it has some exploits in its history, and overall output of the BOINC network in terms of PetaFLOPs is about half that of Folding@Home. BOINC projects are hard to value. People are crunching 10x more RAC on MilkyWay than Rosetta@Home. It becomes a question of priorities. But certainly they have a larger platform to experiment on, like their Neural Network statistics server and the finance project they experimented with. Perhaps what makes GridCoin somewhat confusing to me (and I mine and hold it) is the eccentric relationship with bitcoin utopia whose RAC on the Gridcoin network exceeds the TOTAL out of the network by a factor of 40! Anyway it's all for a good cause, and Bitcoin Utopia did help fund the MilkyWay project and is designed to do "good", but to me, it's just a bit of an admission of defeat when the biggest incentive on a network is to mine bitcoins (with a lower case "b") instead of focusing energy on getting science done.
CureCoin and FoldingCoin (which can be merge-mined) have a single focus to help Folding@Home find drug-able states in proteins related to "deadly disease". They have a more stable history in terms of security. *IF* CureCoin ever gets 2.0 out of beta, it will add value since their new SigmaX blockchain is designed to be quantum computer resistant (I merge-mine and beta test SigmaX so I'm obviously biased in my opinions). But that being said, CureCoin and FoldingCoin are still dependent on one, albeit extremely large, distributed computing consortium of universities and institutions (incidentally Folding@Home is much more than just Stanford and even includes institutions like Hong Kong University of Science and Technology). On a small scale, CureCoin has proven it can be used to help fund it's underlying research without resorting to mining bitcoin. BTW, Nothing is easier for a newb than loading Folding@Home's NaCl client in a chrome browser and registering on the folding pool.
Diversification is always the best bet. I wouldn't be putting my life savings into any of these ventures individually, but they all make an interesting hedge.