No one favorite, usually a few favorites for the year. They are in such different stages of growing, and most beautiful when they are mature (usually 4-5 years). Then there's moles, voles, not enough rain, etc., so that some perform better than others different years. One that I think is under-appreciated because it is an older variety that does amaze me each year with it's pattern and colors is ventricosa Aureomarginata.. If it was a more recent hybrid, everyone would just have to buy it.
I really enjoy the combinations of hostas together in a garden, with the colors playing off one another. Also the different textures and shapes. Sometimes it is the way a leaf sways in the wind. Some of the new ones that hybridizers are showing pictures of on the seedgrower's site amaze me for their number of colors on one leaf, streaks, beautiful flowers, etc. etc
I am about the same way about daylilies. Can't pick one favorite. Love combinations or that they bloom late, or hav amazing color or size or shape. Glad I don't have to pick just one of any plant, I guess.