There are at least 10 versions of GT. All with their own quirks and reasons.
Just the other day a new pack came out, 1.7.10, with tons of quests. I look at the mods it contains, and it has a version of GT I’ve never seen before, a port of GT4 to 1.7.10:
I’m planning to gather all infos on a blog post or something, but the incomplete summary is:
- The last, up to date, version of GT is 6. For 1.7.10. The one currently developed by Greg and so expansive that it’s almost a total conversion. This is rarely found in modpacks. It’s still ongoing but it hasn’t been in heavy development for a while. There were rumors that Greg was planning to make a brand new game separate from Minecraft, based on GT.
- It often happens that big mods change significantly between version. Not always the most up to date is the best, or most complete. A famous example is another of the biggest and best mods in Minecraft: Thaumcraft. The most recent version is 6, but development stalled and it’s not the most complete. Many players prefer 4 (the one used in GTNH) or 5. Or even earlier versions.
- For similar reasons, the more popular version of GregTech is 5. Also for 1.7.10. But while Greg has abandoned 5 to work on the 6th, the community is carrying the torch. This leads to the very popular GTNH, and a significant expansion of GT5.
- GT6 is also being expanded, with a “GT6 Unofficial”. It’s GT6 plus some other stuff. But it doesn’t seem to have lots of activity. I’ve seen Greg complaining that stuff into the pack could have worked better as an add on, rather than a different mod. And he’s also thinking of including some of the stuff right into GT6.
- As I was saying before, lots of work is instead going into a port of GT5 to 1.12.2, leading first to GTCE, expanded through Gregicality, and now to GTCE-Unofficial, that is done by the Gregicality guys. 1.12.2 itself was generally considered an incomplete work in progress otherwise, so the big two GTs were 5u and 6 only.
- There are a few attempts to port GT to 1.16.5. One is Tech Reborn, but it’s only a mod loosely inspired by GT. There’s another mod that is porting GT3 or 4. Some people simply like earlier versions of GT better, even under 5. I suppose both 5 & 6 are way too big and complex to be updated to new versions of Minecraft, so if you want those you are stuck with 1.7.10.
- Minecraft 1.7.10 has 5-Unoffical, found in GTNH pack, and GT6. There’s only an handful of packs that have GT6, and a light one can be found here:
(I’ve used this one to add a huge amount of mods, including all Reika’s mods)
- Minecraft 1.12.2 has GTCE, Gegicality is an add-on to GTCE. Those who work on Gregicality are now doing a total rewrite of GTCE, called GTCE Unofficial. Until then, this is a good pack based on GTCE + Gregicality (you mention the skyblock, which is fine if you want the skyblock gameplay):
GregTech was originally an addon to a larger mod called IndustrialCraft 2. It started in the IC2 forums and the mod depended on it. GTNH still uses the integration between IC2 and GT5. With time GT grew more and more ambitious. Only with GT6 the mod became standalone.
To answer your questions:
GT is a mod, not a modpack. People usually download and play modpacks, because configuring and setting up mods together is very complex. Modpacks modify recipes to blend mods together, provide some meaningful progression, and usually add quests to better guide this progress.
GTNH is a large modpack, where GT is only one component. It includes for example magic stuff like Thaumcraft, but all generally integrated into a sort of linear progression. It does a pretty excellent job to guide the player through the quests.
GTCE stuff is relevant because it moves to Minecraft 1.12.2. Packs like Supersymmetry already have quests. But they are not complete (not complete = there’s still a few hundreds hours of content). Lots of packs have quests, it depends how many, and how much handholding.
I still haven’t played a lot, myself. I think GTNH is good as a guide, but it’s also a grindy pack that demands a lot. Omnifactory should have a very good quest book BUT. This is GTCE (no Gregicality), on 1.12.2. Omnifactory focuses on later stages, and loads you with resources at the start (you spawn with diamond tools, just to give an idea). So it skips most of the survival/exploratory nature of Minecraft. It basically boosts you to an advanced state. FTB Interactions is an excellent pack but also on 1.12.2, and also very different. It get praised because it blends mods together (as the name says), but it also warps them and creates a much different experience from the slow burn Minecraft progression.
Beside FTB Interactions & Omnifactory, as tutorials (but without GregTech) there are FTB Academy and FTB University. Both great packs that tech you stuff through excellent quest guidance (but seek the 1.12 versions, avoid 1.16).
There are lots of great packs that do not have GregTech. Sevtech Ages, Enigmatica 2 Expert. Yesterday I also found this:
It seems to have a great quest book, almost 2000 quests divided by mods. It’s on 1.16.5.
Divine Journey 2 also is a huge progress and quest based mod.
Less quests, but huge tech modpack is Multiblock Madness (one of the few, along with Supersymmetry, to include complex advanced stuff like NuclearCraft Overhaul and QMD).
Crucial 2 should have excellent documentation, for a lightweight pack based on 1.16.5, but not progress based.
MC Eternal is a giant pack, with quests, on 1.12.2 frequently mentioned.
Same for “Dungeons, Dragons and Space Shuttles” and Age of Fate, almost 2000 quests in each, but more focused on “adventure”, rather than tech.
…There are tons more. Greedycraft. MC Odyssey, Ragnamod V, packs based on TerraFirmaCraft…