I am looking for a GPS module for my quadcopter, but there are so many options I don't know which one to get.
There are the BN180, BN200, BN220, BN280 and BN880...
What are the differences between them?

So far from what I've gathered,

BN280 and BN-880 both have a compass (magnetometer) built in. These are pretty bulky for a mini quad.

There are smaller GPS modules, such as the BN180 and 220. These don't have Compass in them however. The BN-180 doesn't have flash memory for saving configuration while the BN-220 does.

If you're just looking for a module to take advantage of the new GPS Rescue mode in Betaflight, I'd recommend this one
https://www.racedayquads.com/products/mi...ps-glonass

Specification of BN180 and BN200 is the same. What is the difference between BN200 and the others?

I've looked into this a little myself, they use the same chipset and as far as i can tell they are all p[retty much the same with the exception of the last two which have a compass, the major difference being the size of the built in antenna. If you are using Betaflight the compass would be a waste of time. I opted for the BN-220 and as long as you can keep the smaller units away from your VTX & antenna you should be ok, which is easier said than done on a mini quad. Mounting is key to getting these cheaper units to work, if you want a hastle free install best buy a matek, they are more expensive but produce better results.

Here is a handy matrix showing the differences: