I would go with ETH because it has the most potential of any alt out there (in my opinion). Smart contracts can transform the way that the economy functions. It is one of the strongest use cases that crypto has.

As an aside, I don't understand the direct price comparison that people make sometimes, e.g. coin A costs £50 but coin B costs $100, so coin A is better to buy. Not sure if you're making this point here, but I don't get it. The price of a coin means nothing without also considering its supply. As an extreme example, if coin A above has a supply of 1 billion coins, but coin B has a supply of 1 million, that makes the $50 coin A huge, whilst coin B is the low cap underdog that offers the potential for growth. Switch marketcap the other way, and positions reverse. Price alone means very little.