Binance would be the best – it’s the number #1 Crypto exchange in the world.
Coinbase would obviously bring a lot more exposure to ETN around the world (especially Aus, US & Europe) due to its ease of use, but ETN is a way too young/untested of a project for Coinbase to consider listing it at this point in time.
Huobi is a chinese exchange that would be nice to get listed on, giving china better access to ETN.
I’m not sure about Poloniex or Bittrex – they seem to have fallen by the wayside a bit.
Keep in mind that ETN is already listed on Liquid (formerly Quoine) – their new exchange has a nice layout and user interface, which should see the exchange grow in volume and user numbers. It’s a more attractive and user-friendly exchange than Binance. The Youtuber AllAboutTech recently made a good video about Liquid, and he seems very optimistic about the prospect of it blowing up to become one of the leading exchanges.
The YouTuber Matthew Gray suggested in one of his videos that the key to driving user adoption of ETN would be to have an option in the Electroneum app to purchase ETN directly with fiat currency. This makes perfect sense – giving people the ability to earn ETN with the mobile miner is a good way to motivate people to install the App, but allowing people to buy more ETN with the simple click of a button would give ETN a massive advantage over other altcoins. If ETN is simple and easy to use, and offers a more convenient way of obtaining the currency than the tedious task of sending fiat to an exchange to buy BTC/LTC/ETH and trading it for the desired altcoin, then ETN could attract a lot more users.