I'm thinking that if you're going to do it, might as well go 20-amp, but it seems that everyone else does 15.
Thoughts?

Do 20a, no reason not to. Those lights just seem to multiply every year. Use a quality receptacle.

Definately 20A... I have 2 20A circuits for mine and had them both maxed out at 80%..... Then they came out with LED lights! Ahh well

There's really no reason to not use a 20 amp circuit for x-mas lights on the outside of the house. The reason being, obviously, 4 more amps can be used than on a 15 amp circuit.

I did a real nice job last month where I ran (2) 20amp branch circuits (1 for each outside GFI receptacle location), and had them operating off of a single pole, double throw T-103 time clock beside the panel. The customer was very happy with the work I had done too, :-)

T-103-70 Intermatic?
DOUBLE pole SINGLE throw 120V clock motor ya mean?
Sorry, flashback to the days of workin behind the "counter" LOL

A.D

Yes, double pole, single throw. My bad. What the hell was I thinking?

Oh, and I'm becoming very familiar with some of the model numbers for a number of products I use. For 11 years with 1 contractor, I never had to do any paperwork - just the actual work. Now I'm with a new company and I have to write down a code number for nearly everything I use! It's actually a pretty good idea to know the numbers of products used because the guy at the supply house most of the time knows the number but has no idea what the product is used for. Not all of them, but some. Don't mean any disrespect to the counter guys here :-)

A little calrification...

"Holiday lighting package" in new home construction means installing an additionla receptacle in the INTERIOR of the home at each front window, all on the same, different circuit than the general purpose receptacles, and all controlled form the same switch.
Usually, the most that will be plugged in each will be a single, or possibly a triple decorative candle fixture at about 25-40 watts each lamp.

REdsy:
Had one of them in a McMansion about 2 months back....EC did it in 12, had about 4-5 circuits....sw in each room, sideways duplex tucked right at window sill; 1/2 switched.

($8 mil ponderosa)

John