I have been using mockups for my entire design career. I started with business cards, then stationary all the way to devices. I find it painful to find the best mockups in one place, especially if you can only afford the free ones.
After a while, I realised an investment on a great mockups bundle will save me a lot of money and that's when I found ls.graphics. They have the best mockups in the game, both for graphic designers and digital designers. Their Unlimited Access account is on offer for 99$ instead of 179$. It includes $1552 worth of assets and future releases for 365 days.
Invest in this great pack and trust me, you'll thank me later. Get an Unlimited Access account here.
If you can't afford it yet, check out their free mockups!