So in a nutshell Xbox 360 and PS3 are obviously the older models, perhaps 7-8 years now so in my opinion it makes sense to invest in a next gen console like the Xbox One or PS4, it is mostly where the game developers will be focusing on in the future. They have better CPU/GPU, graphics card, storage and generally speaking more potential for the next 5 years or so. Now PS4 vs Xbox One is a different matter, pros and cons for both the most common opinion is PS4 for gaming and Xbox One for multimedia.
I’ve had a 360 and loved it, I purchased the Xbox One on launch and sold it two months later, I felt let down to be honest so as soon as I have bought the rest of my bike kit ill be investing in a PS4.
There are lots of both on eBay so I wouldn’t worry too much about getting one new, I was looking yesterday and PS4’s tend to sell around the £250 mark. I hope that helps.