Of course USB-AC68 is better.

http://www.blacktubi.com/review/asus-usb-ac68-review/

1. DIR-850L is 2x2 ac router, so you won't be able to make use of the 3x3 capability of AC68.
2. If you're using PC with available free PCI-E slot, I recommend using PCI-E wireless adapter instead of USB. USB 2.0 & some of so-called USB 3.0 wifi adapter rely too much on your CPU & may have latency issues when your PC is on heavy load, which is bad for gaming.
3. If current 2.4GHz wifi signal detected by your pc is lower than about -60dB, you won't get high data rate with your ac wireless as 5GHz signal strength will be lower than that (5GHz had lower range than 2.4GHz at same power level, and had higher attenuation from walls blocking the signal) and require a good signal strength/quality in order to have good data rate.
4. My advise, don't so hung up on utilising the entire bandwidth by yourself especially on wifi. Realistically, you probably need additional access point if you want to make full use of the bandwidth across multitple wifi devices. If you are so keen on monopolising the entire bandwidth to yourself, then just use gigabit ethernet connection.

Number 2 I agree since I have usb-ac68 but for number 3 mine is a special case, 2.4GHz getting around -60 to -73 while 5GHZ getting stable -49 to -52 at the exact same location. Plus for number 1 better for future proof as ac1900 will most likely the best price/performance ratio since mu-mimo is dying. But number 4 is so true, nothing beats ethernet at latency and consistentcy.

From my experience, you can try getting Archer T9E,

quite reasonable.

Thanks for all the suggestion. I am going to buy a super long ethernet cable and then connect it to my PC. So, even though my motherboard cannot support 5G, using the ethernet cable will allow my PC to fully utilize the 300mbps right?

This post has been edited by LeoLilieno: Nov 23 2016, 08:46 PM

300mbps = ~37MB/s

Be sure LAN cable is CAT5e (for the best, get an CAT6)
also PC and Router have Gigabit Ethernet

for WiFi method, get an USB 3.0 or PCI-E Wireless AC, Router also need support Wireless AC

USB 2.0 speed is 400mbps in full-duplex,
but USB 2.0 communication in half-duplex, which mean 200mbps (~25MB/s)

My router is My router is D-Link DIR850L. Can it support Gigabit Ethernet? This is so technical . I thought all I need to do is buy the normal cable, make sure its long enough and then plug in.

just get a good wifi adapter at your side D-LINK DWA-182 (high end) or D-LINK DWA-132 (low end) will do, no need cable la nowadays. your router no problem.

But my motherboard is an old motherboard (3yrs plus model) and I am afraid that I beli wifi adapter and then tak support pulak.

brother, my super old pentium also support usb wifi adapter, what u said

For maximum stability I recommend Ethernet Cable, cat5e is good enough .

What I meant was, I don't to ends up spending hundreds of ringgit to buy a high end USB WiFi adapter and then only realise my PC can't fully utilise its speed.

I bought a USB WiFi adapter that says support up to 300mbps BUT when I plug in to my USB3.0, the speed still average at 40mbps.

You've misunderstood about the difference between data transfer speed and the bandwidth.

Technically the WiFi adapter's 300 mbps is just data transfer speed. generating the transfer between your packets being sent and received. which is why more data transfer speed = suiting more data transfer through the internet speed.

Based on D-Link webside, your DIR850L has Gigabit Ethernet,
http://us.dlink.com/products/connect/wirel...outer-dir-850l/

I recommend you buy an CAT5e LAN Cable,

on my test, I can transfer file between computers almost 70MB/s (~560Mbps)

If your old computer don't have Gigabit LAN, get this one:
http://www.tp-link.com.my/products/details...11_TG-3468.html