AMD releases their Vega cards in a few months, which will probably have performance similar to the higher end Nvidia cards (1070, 1080, 1080ti, etc). Prices of Nvidia cards currently often have pretty good deals on them to account for that, though once the Vega cards are sold out Nvidia will probably price hike again.
Intel cards generally perform better in single threaded applications, while Ryzen is better for multithreading. This is a big simplification and there's lots of specifics involved but that's not a big deal for you. In terms of games, they're generally pretty reliant on single thread performance, even if they do make use of multithreading. If you go top of the line in either, it won't make too much of a difference in the majority of games, especially if you're just doing 1080p 144hz. However, if you multitask while gaming, such as streaming or watching video or something, then Ryzen will be better for those scenarios.
As an aside, I think you should really take the time to build your own PC if possible. Like others have said, if that's not possible for you then you can pay to have your parts assembled at a much lower premium than ibuypower. It's nice to know in depth what's going into something that is a major part of your daily living.
edit: I was wrong about Vega release date, gaming specific cards aren't out until probably q3 2017.