I use Jaxx Wallet for that purpose. Pretty straight forward to use
EFT some cash to Luno, buy some BTC and send it to Jaxx, from there you can "shapeshift" BTC into various altcoins, including ETH of course.
Naturally you can also "shapeshift" ETH into BTC and various other altcoins.
No idea if this would be considered the "BEST" approach, but that's how I currently do it, plus I haven't tried anything else, so wouldn't know.