My favorite print recently have been duplo blocks that I reverse engineered and built back up in freecad for 3d printing. Here’s an overview of the pieces Ive modeled. Some were based off https://www.printables.com/model/137952-lego-duplo-compatible-building-block-2x2 originally and I used tinkercad to modify the model to create better clutch and fitment. Eventually I went full calipers on my kiddos duplos though and created a master sheet of dimensions that Ive used now in FreeCAD to remake everything. Toying with fitment and clutch has been a lot of fun as well as modifying the pieces for 3d printing.

In a very similar vein I spent a lot of time perfecting settings and orientations on this Lego Crocodile model https://www.printables.com/model/943591-lego-compatible-6026c01dat-animal-crocodile-comple/files

My kid absolutely love that I can print him out duplo pieces on demand.

As for practical this phone stand Ive really been loving https://makerworld.com/en/models/868130-herringbone-gear-phone-stand-pork3d-by-pork3d-com

Honorable mentions are the shelf I designed to hold my things along my desk and little figurines Ive been starting to toy with. Learning how to print things no designed to be 3d printed or modifying to print cleanly is really a fun challenge Ive found.

Thanks everyone for their shares, too! I def gonna print that hammer for a lighter touch than my engineering hammer.