Well, bitcoin is the best crypto and considering the current market it would be the best choice. On the other hand, i really don't have much idea about Iota.
Bitcoin is always an option in crypto investment. but, I might share the money for 4 crypto, bitcoin, eth, xrp, and bch. well, the coin is a very good coin, and stable enough to be stored in the long run. besides, bch coins are also good for short-term investments.
Bitcoin isn't an option, it is the best to invest among the entire cryptocurrency. As mentioned all that provided is good asset to make an investment, except xrp. Apart from these I believe to make investing on IEO and ICO. Along with the same I prefer to segregate assets for long term and short term investments.