Astronerd :
WIFI can be a very tricky thing... On one side you have the theoretical possibilities and on the other the environment in which your system operates. For example, if you are surrounded by many access points, your system won't be able to aggregate the frequencies to achieve the 40Mhz needed by 802.11n, so you'll be stuck with your basic B/G mode. And if you want to use 802.11ac (5Ghz), depending on your environment again, your link can be VERY fragile.
For 802.11ac mode , you need to have 802.11ac on both computers, the Raspi (only the 3 B+ is capable of ac) and your laptop. The simple 3B doesn't even have a 802.11n mode ( "iw list" gives you HT20 only, no HT20/HT40 ).
So you need to measure the performance of your link FIRST. Once you have measured the problem you can find a solution. Start with "iwconfig" to see the speed of the link. It should at least be 150Mb/s if you want to transfer images from a DSLR or ASI1600/ASI183 (BIG images). Then, try the "iperf " command (see my message above).
If you get a low transfer rate (under 80Mb/s), then you need to find another solution, like a WIFI/USB antenna with a high gain. A simple dongle won't probably do a much better job than the internal WIFI chip.
The best solution I've found so far is a small AP device you plug in an AC outlet, linked to the PI by an ethernet cable. It has a built in HTTP server, so you can easily tweak your connection, set a passphrase , change the ESSID, etc.... On a 3B+, you can expect up to 300Mb/s.
Of course, the major inconvenient is ... Well, you need an AC outlet nearby.
- Marc