My most recent favorite is All You Need Is Love by Dani Mogstad - I could just keep using that kit over and over!
But I'm really fickle normally when it comes to kits - whatever's most recent is my favorite, usually. Recently I've been going back to:
Frosted Flakes by Dani Mogstad
Flower Stand by Scrap Kitchen & Shabby Miss Jenn.
The items that I keep going back to most are non-kits, though –
Dotty Alpha by Fee Jardine,
Going Places Alpha by Misty Cato,
All Worn Out: Photograph and Paper Overlays by Penny Springmann,
Frame It by Melissa Bennett and
The Ultimate Stitch Collection by Dani Mogstad (though if I didn’t have that, I’d be going to Traci’s Bad Sewing Machine series).
But I haven't started playing with the couple items I bought over the weekend, and I still plan on using my Sweet Rewards, so my favorites just might change soon!