I'm sure everyone here will suggest Bitcoin and Ethereum for the first couple, because we know that almost everyone uses Bitcoin and Ethereum. And as an advanced option you can choose several coins with a high level of popularity and one more, don't forget for the USDT pair.
EOS and Neo can be a good choice too , or Waves they have potential growth through the use of their platforms that can be a big help for early adopter.
but for myself the crypto pair that I use is bitcoin and ethereum because my dream can get a big profit from both of these coins and both of these coins are also many investors who trust