The answer to this depends on various aspects. If you have the money for a Tesla it is an obvious choice regardless of whether or not you care about doing something to help the environment.
If you don’t have the money for a Tesla but can stretch to afford a Nissan Leaf or similar priced car, and you do enough miles to make up for the monthly battery rental, then it is probably a no-brainer for you as well. Regardless of how much eco-guilt you feel when driving a petrol or diesel car around. As long as you don’t need to do very frequent long trips.
If you can stretch to afford a Nissan Leaf / Renault Zoe type car and you do low mileage that would amount to significantly more in battery rental per month than your current petrol expenditure, then you, like me are an eco-nut. But in your mind it will probably be a no brainer as well.
If you can’t afford a Tesla, need to do frequent long journeys and have no patience to wait around while rapid charging, I would suggest a BMW i3 REX if you can afford it. If not, maybe some other high EV range plug-in-hybrid like a Chevy Volt, if we get that in the UK.
If you can’t stretch to a Renault Zoe with battery rental and you don’t care about the environment, then it’ll be a bit of a wait. Maybe by 2022 you’ll be able to buy an EV and run it with no battery rental at a cost lower than any petrol or diesel car. It may happen before then, it may take a little longer, but I would say around 5-6 years is a pretty good bet.