This is gonna be tough, but let me try.
Colours:

Purples, Greens and bright shades of blue and yellow/orange.

Browns usually get me bored fast.
Threads

Anchor and DMC.

Metallics in general.
Fabric

Aida - 14ct (love how Jobelan feels but am working on evenweave for the first time since the 80's so am not familiar with it yet enough to really enjoy it)

Linen
Patterns

Fantasy, country stuff, cats among many others.

Most lifelike portraits of people (some are great though), most floral table runners (a lot of those patterns look very dated to me) and religious designs.
Kits

Dimensions make fantastic kits, like their beach stuff, wizards, country designs, etc.

Kits with printed designs on the fabric, especially those where some of the fabric is printed to be covered in stitches and the rest to remain just painted.
Things I would like to try - Working with different threads like silks, and getting used to evenweave as some of my projects would look much better on it. HAED designs (got a small start on it).