Now a days if you want to mine bitcoin you need to use an ASIC miner (antminer S9).
Most GPU can only mine alt coins now since mining Bitcoin using it will not be profitable.
Downside of an ASIC miner is that it consumes a lot of electricity and it don't have other
use but mining Bitcoin.

GPU's can mine altcoin if there is a coin that is worth mining then I suggest better go with this.
Warranty is until 3 years and in case mining is not profitable it can be used as a Graphics card for your PC's