I opened once as soon as i got 2,590 diamonds and pulled Riley and Garrick card. i was super happy at that moment as i didn't know both can be obtained from gold chest lol
However, Riley helped a lot to proceed at low level
Lucky you. I opened maaaaaaaaaany gold chests and I didn't get Garrick at all. I had to summon him once I got to Epic Arena
Anyway, opening 10x diamond chests is very good. The first month of playing, buy the monthly chests card. Open a 10x pull every 10 days. It will give you a huge boost!