hello, i'm new to mining. i have a r9 280x and a i5-4690. i was wondering what's the best currency i can mine with this hardwere.
From what I've read on the internet it mines ethereum at about 15 mh/s. But consumes almost 200 watts.
How much you pay for electricity is a main factor. Check this
LINK and input how much you pay for kw/h and you'll get the approx. profits per month.
what's the difference between cpu and gpu mining ?
They both mine coins but basically gpus have much more computing power in mining than cpus. Actually cpu-mineable coins now are few and are almost not worth the hassle as the profits are too little.
If you want to mine use a gpu card otherwise don't waste your time.