Hard to tell, honestly. It depends on which parts of the 6th world you are interested in, if you are looking more for inspiration and game hooks or actually usable rules and stats, and how much you want to moderate what your players can use for themselfes.
Parts of the Core rules are so shoddy that they hardly work without the supplements. This is especially true for Rigging and Matrix Stuff. If you want to feature this kind of content, you should have a look into
Rigger 5 and
Kill Code. Both are not flawless, but make things a lot better at this end. The first Matrix Supplement
Data Trails is really weak when it comes to actual rules, but it came out before Kill Code, so you might have troubles understanding some things featured there without it - Itīs a stinker, but somewhat necissary...
(Thatīs my opinion on the Matrix and Rigging content, though. Donīt want to argue

)
When it comes to the other Supplements:
- Street Grimoire: Solid. Mostly new options and flavours for Magic Stuff, few game-changers.
- Forbidden Arcana: Second Magic Rule book, more "crazy" and "edgy" options. Cool stuff, but some things are thoroughly broken. Use with caution and prepare to say "no" to your players, especially summoners.
- Chrome Flesh: Lots of Augmentations, including Nanotech, Genetech etc. My favourite so far. Really crunchy without stuff thatīs too broken. The "edgier" options for augmentations (Cyber Zombies, Cyborgs) and some "classics" are still missing from the game, though. I suspect that thereīs a second Augmentation book to be announced in the future, but thatīs just a bold guess.
- Run and Gun: Solid. More Guns, Clothing and Accessories, Martial Arts, Combat Options, Rules for Survival. Itīs a players favourite, but I think itīs really not that usefull for GMs. For NPCs, you can just stick to the options in the Core rule book or make up stats.
- Street Lethal: Run and Gun 2.0 - Electric Boogaloo. Yet more Weapons and Stuff, including Sci-Fi-Prototypes that are not on the open market. Really not worth the money, even for a GM. Adds almost nothing that other Supplements donīt provide better besides the Weapon prototypes, which are meant to be McGuffins anyway. If youīre a reasonably competent GM, nothing stops you from scribbling down some stats for them yourself.
- Howling Shadows: Good choice for a GM of you want more non-human opponents in the game. Biggest complaint back then was the missing price list for animals, which you donīt have to care about as a GM. Contains a section about AIs that you canīt use without the gruesome Data Trails rule book.
- Dark Terrors: More eldritch threats to use as a GM. Bit of a mixed Bag, better look into Howling Shadows first and decide for yourself if it satisfies your needs.
- Complete Trog: Absolute waste of money and time, unless you are really into Orcs and Trolls.
- Smoking Aces: Face/Social Book. Save your money. Lots of boring fluff, and the few actual rules only make things more complicated. Best part is probably the spy equipment. But seriously, if your players or NPCs need a Pen Knife or stuff like that, just make up a price and some stats. No need to buy this.
- Hard Targets: Book for Assasins. Pretty much the as with Smoking Aces and Complete Trog: if you are not interested in lots and lots of fluff about the topic, donīt buy it. Some Qualities and weapon mods in the rules section are funny to play around, but thatīs not worth it on its own.
About the Mini-Supplements:
- Bullets & Bandages: Advanced Medicine rules. Neat little thing, might be worth the small price if you want to make patching up after combat more interesting. Also provides some interesting threats like toxins and drugs to thow at your players.
- Gun H(e)aven 3: More Weapons, simple as that. The problem with all the Weapon books is that the hardly add anything new, though: Itīs always just some numbers pushed about. As GM, nothing stops you from doing that yourself if youīre not happy with the Weapons in the Core Rule Book
- Aetherology: Bwahahahahahahaha. No. Absolute Drek. Nothing of value unless you have a group that exists entirely of full Mages and unless you have no grain of creativity on your own.
- Shadow Spells: Mini-Supplement to Street Grimoire. Some funny new spells and Adept powers for a relatively low price. Iīd recommend it.
These are the ones I can offer an articulated opinion on. My best tipp would be to dip into Chrome Flesh or Howling Shadows next, or into Rigger 5 and Kill Code (and Data Trails *sigh*...) if you want to patch up the "Cyber" part of Magicrun
