While the final release of Destiny might differ a bit from what everyone experiences and sees during the beta, we've already gotten a sense of how the different versions of the game will visually compare.
Obviously, something on a last-gen console won't look as hot as a current-gen console release — as you can see in this video by DigitalFoundry. Still, the game is gorgeous on both platforms. It's also worth remembering that you can transfer your saves from last-gen consoles to current-gen consoles, should you buy the game on the PS3 and then later decide that you'd like the prettier version instead.
Destiny Beta: PS3 vs PS4 Comparison [DigitalFoundry]