I don't do the pre-lit trees, but I can speak for the LEDs. Great electricity savings! I replaced the 10 strings of C-9s we use on the outside of the house with LEDs a few years ago and I'd estimate it saves about $100 during the holiday season. I used to have the C-9s burning from about 4:30 (dusk) until midnight every day, but then scaled it back to about 5-9pm. With the LEDs I have them back on the old schedule.
I do like the older lights for the "homey" glow and we still use them inside, but they're really only on in force during parties.
Chuck