There is definitely no lack of choice if you're shopping for an external WiFi adapter, however the performance between the models differs about as much as their price. We do want to note that the most expensive USB adapter and the most expensive PCI-Express plug-in card are also the fastest models, while the cheapest ones are also the slowest - however this does not mean at all that there is a correlation between price and performance.
Out of the USB adapters the ASUS USB-AC68 is by far the fastest. It's not cheap, however those who want the best of the best don't have to look any farther. An Ultimate Product Award is more than deserved. If you want to spend a bit less, the Edimax EW-7833UAC is almost just as fast, however it's priced much more attractively. We're awarding it with an Excellent Choice Award. If you're really shopping on a budget, there are still a couple of interesting options. The D-Link AC600 High Gain is the best of the cheaper adapters, the Eminent EM4535 is couple bucks more expensive, but also significantly faster. Both receive a Great Value Award.
If you're looking for a practical and small adapter, the Sitecom WLA-3001 is worth considering - the TP-Link T1U is even cheaper, however we weren't able to establish stable connections with it. Even though the integration of a bit of storage to include the driver directly on the stick is not very new, we do find the feature recommendable enough to award AVM with an Innovation Award for the Fritz!Wlan AC860.
Choosing between the PCI-Express adapters is not very hard. The expensive PCE-AC88 offers the best performance, which means that it receives an Ultimate Product Award. The TP-Link Archer T9E AC1900 is priced much nicer while still performing really well, therefore it goes home with the Excellent Choice Award. The other test participant from TP-Link - the Archer T6E - stands out due to its decent performance for a relatively low price and therefore it receives a Great Value Award.