Best kits I've brewed (with related tweaks):
Evil Dog Double IPA with 100g lemon drop added to the "tea stage" alongside the included hops. The original beer is a bit low on hop aroma for my tastes, so I did this the second time and it is lovely.
Tinsel Toes with an extra can of LME. The advertised 4% wasn't what I wanted out of a winter warmer, so I amped it up a touch. Great stuff, and at 6%, nice and warming too. Probably going to be making this again in time for Christmas.
Mangrove Jack's Grapefruit IPA was the best untweaked kit I've done so far, but I'd like to add some additional citrus flavour somehow if I did it again (grapefruit oleo saccrum after the primary fermentation dies down, maybe).
One more vote for Wherry too, its a good kit.