in my opinion, there is no crypto that will be stable because none of the crypto guarantees fixed assets such as gold, silver or oil that are at market prices. Their fluctuations are based on international market standards. USDT / USDC will be stable when we live in a country that uses dollars, other than that country will experience the same fluctuations.
Well I think there is no such crypto currency that you can bet your 100% on it.
You have to do your own research which coin is good and has the future.
Study about the platform on which it is being developed.
Study about the problem that they are trying to solve.
Check out the leadership team and their profiles on linked in.
Total Number of coins that is going to be circulated.
These are just the initial steps that you have to take into consideration. I would suggest you to eye for an ICO(Initial Coin Offerings) which will provide you with a chance to buy the coin at less price.Honestly it's hard to say as of now which cryptocurrency is most stable because as we can see now in crypto market all cryptocurrency is getting up and down.