Some of my current favourite series include Parks & Recreation, Downton Abbey, Blue Bloods, Madam Secretary and The Musketeers. Honorable mentions are Castle, Lewis, Homeland, Designated Survivor and Brooklyn Nine-Nine.
I find I enjoy series that have an element of mystery, humour, history and/or political intrigue. I used to love fantasy series like Charmed, Buffy the Vampire Slayer, and The Shannara Chronicles, but in the last few years I've been moving more towards the other genres I mentioned. It is interesting reflecting back on how my tastes have changed over time.