Favorite and least favorite puzzle elements to use in maps?
I find myself using Gels, Funnels, Faith Plates and Lasers the most. I don't use crushers cause I think they are cheap and because I can't get them to run right, and Hard Light Bridges. The Funnels are cooler.
More information Here
"Pretty is better than ugly, but if it doesn't work, ugly is better than pretty"
-Phyton
I really like Faith plates. I love to fly! 
Also using the portals and portal-flings as a puzzle is also a good thing. Some levels doesn't contain any challenge using portals.
I, like plenty of people here, don't like massive amounts of turret. It's ok if i have to knock out 1 or 2 but 20 is just getting boring.
My favourites - Excursion funnel, lightbridge, emancipation grills.
Dislike - Turrets, laserfields (even though my only released map is covered with them!), faithplates and flings with momentum.
The discouragement beam is one that I can love OR hate. If used properly, it can be a great puzzle element (a good example would be the DLC - chambers 7 & 9, execellent use of the laser). However, laser-tests with multiple relays and multiple reflectocubes - I simply despise.