I'd say it depends on what you're looking for. Destiny used to be "Become Legend", a power fantasy, but I think it has lost most of its identity apart from the gunplay and the synergies with the movement and abilities. If you're looking for a good time with a first person shooter mowing down enemies, blowing them up, and finding particular god rolls from loot, then Destiny. Whereas Warframe seems more like, "How far can you push beyond the game?" Build crafting is almost limitless, and the varied playstyles/modes allow for a wider playerbase. Not to mention, there's much more augments and synergies tying your character abilities and weapons together. Warframe definitely feels more like a numbers game sometimes though. For me, personally, the better game is whichever one that keeps me coming back the most. That falls to Destiny, albeit, I also get so very frustrated with the state of Destiny 2 compared to Warframe where I'm generally content with the passing states of the game.