To be honest, it really depends on what you’re playing. Bots battles last 5 minutes and you rarely get past level 6 or 7, so taking a shard genny and two decent purples seems about right. For missions, you might play 25-35 minutes, but even then, the shard count can change drastically. Like, Demon Bear has around 8 or 9 total shards on the map (seriously, it’s stupid), but Heart of Ekkunar has literally unlimited shards. You can run 3 legendaries in Ekkunar, or not activate a single one in Demon Bear.
So, personally, I have two rough sets - five-ish loadouts of a shard genny and two purples for, and then a bunch of character specific loadouts for the longer missions.
You’ll get a lot of answers here, but generally, the Symbiotic Gauntlet is pretty much good on every single character (9.1% attack damage, +280HP, +9.1% more attach damage based on current health), Bola’s Target Finder is good on almost everyone, and if you like healing, Symbiotic Spores is great.
For other legendaries though, I would strongly recommend you use a Legendary if and only if the “Legendary Bonus” is absolutely worth it. Most legendaries are simply purple items with a “Legendary” bonus tacked on, but lots of times, those bonuses are simply not worth it. A good example is Vyn’s Quiver. The difference between Vyn’s and a Purple is that Vyn’s gives you a short burst of health regen if you reload your gun before it’s empty. But I’ve tried it, and it doesn’t even kick in unless there are ~8/10 rounds in the clip, and yet I see Benedicts, Ernests, and so on using it from time to time, when they physically can’t take advantage of the bonus because their clip size is too low to begin with. Now, maybe it’s a bug, and it should be based on % of clip remaining, not a static number of bullets, but for now, even if yo’re running a char that can use it, I still doubt the utility of a short regen in exchange for lots of shard cost above an equivalent purple, a change to your playstyle (reloading earlier than usual), and gimping your damage output (as you spend more time reloading).
But … you’ll need to figure out what works for you.
In terms of what you should always toss, that we can help you with. Nearly all blues and greens have limited value. (not all, but most). You should have a majority of Legendary, purple, and white items. Anything that has a negative that’s bad on every class you can pretty much toss (-max HP, -damage, -move speed, etc.)
In the end, I have ~350 items, but I use maybe 20-30 of them. As far as I know, I have every possible purple and white with max rolls on 99% of them. I’ve got all character legendaries, all story legendaries, all of the ops bossdrop legendaries, and most of the gearpack legendaries … and though I keep them just because, I don’t need them. That said, adding gear back pages using basic credits is pretty easy.
In addition to the legendaries mentioned above, and the 4 0-cost shard gennys, I’d say that I most often use the following purples:
+14hp/sec regen, +5.6 damage
+9.1% damage, +210hp
+9.1% skill damage, +210hp
+attack speed, +210hp
+21% reload, +7hp/sec reload
Again, there are lots of others that have good use, but are often character specific. I won’t try to name them all.
One final thing - not all stats are created equally, and not all stats pair together. You will never find +reload and +hp, for instance (aside from perhaps some weird legendary I’m forgetting). Legendaries are Purples with a special bonus. Purples are Greens with no “activation” clause. And all have a major skill / minor skill. For instance, purples with +HP can be either +280hp (major) or +210hp (minor). For HP, 210HP is 75% of 280HP, but for attack damage, the major and minor are separated by 60% (9.1% and 5.46%). This leads to items with HP as a minor buff somewhat better, and attack damage as a major buff somewhat better. I.e. 280HP + 5.46% attack isn’t quite as efficient as 9.1% attack +210Hp. So, there are lots of nuances that you’ll pick up along the way.
Good luck! And remember that a lot of the fun is learning for yourself what works for you.