Only 3 tweaks? I'll do my best to cut my list down to 3 categories of tweaks, and even then I wouldn't upgrade until iOS is jailbreakable for all the rest. But here goes:
1. Activator, including all the toggles, especially:
BrightVol
appslide
SpringFlash
SBSettings Toggles (especially rotation lock)
LastApp
Monocle
2. SBSettings, including all the toggles, especially:
Data
Location
WiFi
Rotation
Airplane
3. Web enhancements, especially:
FullScreen for Safari (love the customizable gestures)
Bookmarks+ for Safari
GridTab for Safari
Nitrous
PDF Printer for Safari
Platinum
Safari Download Enabler
Safari Upload Enabler (I wish this worked on iOS 6)
Tab+
Universal Video Downloader
Webscrollian
WiFi Passwords
Okay, that's 3 categories, and I haven't even mentioned 2 of my favorite tweaks, AskToCall and DisableNC+. And I think I still have 2 more major categories.
4. FolderEnhancer, alongside:
MultiIconMover
AlwaysClose
IconRotator (or SBRotator, which is not fully compatible with FE)
KillBackground
5. Keyboard tweaks, such as:
DismissMyKeyboard
SwipeSelection
SwipeShiftCaret
DeleteWord (or DeleteWorld, which is not yet iOS 6 ready)
ShowCase
I haven't even mentioned Attachments+ for Mail or AppStore Update Size yet, and I just realized I have a 6th category as well.
6. Visual customization, including:
FakeClockup
Prime
AntiTint
Emphasize
DietBar
DietBulletin
FullImage
PhotoInfo
And I still haven't listed AnyLockApp, Brightness Icons, and DisplayRecorder. Plus I kind of think native tethering is exactly the kind of thing Apple might suddenly insist upon with all its leverage against carriers, since they'd still be getting paid for the data anyway.
Well, that is way more than 3 tweaks, and I have plenty of others not listed. So, I guess I am terrible at this thread. I am truly the worst.
tl;dr
Dear Apple, please hire Ryan Petrich as your Chief Executive of iOS Features.