I won't get into the technicalities of which came first, looks best, etc. I will only say that at the present, all Spyder bags are some sort of add-on, and also that beauty (and functionality) is in the eye of the beholder. What you have to consider are yours needs and desires.
I think the I7 mounts for the GIVI bags were the first. I7 offers mounts for the V35 (PLX) bags, but also for the E21 or E41 (PL) bags. I think the E41 bags have more capacity than the V35 bags do. Turn signal extensions are off the rack, in an intermediate position, as I recall. Racks are not removable unless unbolted. Bags are removable.
The GIVI racks are only offered for the V35 (PLX) bags. Turn signals are remounted to brackets on the rear fender. If you are thinking of ever going fenderless, this is a consideration. Turn signals end up fairly low. Racks are also not removable without tools. Bags are removable. Bags sit a little higher with the GIVI racks.
The BRP bags are licensed to BRP by GIVI, and BRP has made minor changes in badges and reflectors. The racks use the SW-Motech quick-connect system, and are likely licensed to BRP also. This technically makes them a dealer accessory or option, as opposed to an aftermarket add-on. The mounts and turn signal extensions are very obviously designed for the Spyder, and BRP engineers likely did it themselves, or at least had a strong advisory role. Turn signals sit highest of the relocations, at taillight level. Racks are quickly removable with an included special tool. Bags are removable from the racks.
The Corbin bags are designed especially for the Spyder, and accentualte the styling. This is a top-opening bag, unlike the side-opening (clamshell) GIVI versions. Largest capacity of all the bags. The opening width is not the largest, however. Turn signal location appears to be the widest available, but I haven't had an opportunity to compare in person or measure. Turn signals are sunk into the bags, and to me, less obvious (or visible). They certainly are the most stylish. Both racks and bags are not readily removable.
Another consideration is the need for a topcase. The I7 racks have a topcase rack available. I don't think this can be fitted if the BRP backrest is used. Givi offers a separate topcase rack for the standard tailpiece. Kewlmetal offers a rack, but I don't know how it mates with either a sidecase rack system or the BRP sportrack & backrest. BRP does not offer a topcase option, but the GIVI topcase rack would not interfere. Corbin offers a smugglers trunk or a trunkbox, both apparently compatible with their sidecases.
We have the BRP bags, which were purchased for a reason. First, to get around with all the bikes in our garage, we required removable bags. One bag comes off every night, as does the facing bag on my BMW. That way we can get between the machines. We also needed the racks to be removable, in order to reduce the width enough to load a couple of bikes in the trailer along with the Spyder. Others may not have this need, of course. Finally, I am used to clamshell opening bags. I prefer the ease of access over the top opening bags. This is strictly personal preference, and what I am most used to, although I have had the other type. There are many people who feel the opposite way. Although not purchased for the turn signal location, I really like it. It makes them very visible.
Assess your needs, compare the features, prices, and looks. I'm sure you will make a good decision after that.