Which one is the best? I am looking for the best 'N' band adapter. The 7260 has only two streams and its the newer model. Theoretically, it shouldn't perform well compared to 6300 because the later has 3 streams. Or does the newer 7260 has something new which makes it superior to n 6300?
IMO, if your laptop doesn't have 3 antennas, save money and get the Intel dual band 7260 N. You'll get around 170 - 180 Mbps absolute maximum throughput with that card on a 2x2 antenna stream configuration + 40 MHz channel width. If your laptop does have 3 antennas, then choose the Ultimate N 6300 card without a doubt. More antennas = More range and better performance at longer range.
The difference between the 7260 and 6300 is that they use different drivers and that the 7260 prioritizes energy efficiency while 6300 prioritizes performance.
At the same 2x2 configuration, the 6300 and N-7260 will perform about the same or the 6300 might outperform the 7260-N at longer range.
Also, the 7260 might not work with your laptop or will perform "glitchy" since it is intended for Haswell chipset and architecture. Using 7260 on a non Haswell architecture results to WiDi not working. Also, some laptops have their BIOS whitelisted in order to comply with FCC. If your laptop has a BIOS whitelist, the 7260 nor the Intel 6300 will work. Note that if your laptop has a separate Bluetooth module and you put a 7260 N with Bluetooth bundle, your laptop will have conflict with Bluetooth since you will have 2 Bluetooth devices installed. So if you decide to buy the 7260 N, you must make sure that you purchase the one without the integrated Bluetooth unless your laptop did not have Bluetooth initially. The 6300 does not have integrated Bluetooth so there's no need to worry about Bluetooth issues.
The Intel 7260 that does not have integrated Bluetooth has the model number "7260HMW NB"
The following link gives you a one on one product comparison:
If you are looking for a wireless adapter replacement we suggest getting in contact with your system manufacturer for a list of validated adapters and its proper integration.