A hard question. Argaubly, one could say that Bitcoin has a ceiling somewhere equivalent to the worlds money supply. This limitation does not exist on Ethereum ( any number of block-chain applications can be started). Arguably, Ethereum is more general, as it is not really a currency, but blockchain-supported cloud applications. https://cryptonewstrends.com/ So, simplistically, you could say that Ethereum has no real upper limit, further, Ethereum is much earlier in it’s development, and might have further to go in order to reach market saturation than Bitcoin.
So, to summarize:
In favor of Ethereum:
More general, potential larger market
Earlier stage, further to reach saturation
In favor of Bitcoin:
Probable higher usage from common consumers (more people know what to do with Bitcoin/higher uasbility for the general public (most people will not want to start an immutable cloud application))
For me personally, I am heging when it comes to Eth vs BTC… So a bit of both. As they are not directly competing, they can both very well also grow in parallel.
As for choosing crypto-currencies, I tend to select ones that actually bring something new to the game, and have a certain novelty factor. Examples of this include: Ethereum (immutable blockchain-supported cloud applications), Siacoin & Storjcoin (Blockchain based p2p storage), Dash (Faster transfer speeds through master-nodes (as opposed to Litecoins change in block size), in-built anonymity, a portion of each block going to developers of Dash infastructure etc…).
What I stay away from are pure clones, or that try to fix problems that don’t really exist… Examples: Litecoin (supposed increased security and transfer speeds, but Bitcoin has not been shown to lack security, competes with Bitcoin, but not really adding anything new), Feathercoin and the hundreds of other Altcoin popping up every day that dont really add anything new