We are visiting Monument Valley, Arches National Park and Mesa Verde in mid-May. Also want to see some of Canyonlands. Only have time for one section in Canyonlands. Which is easier by car--Island in Sky section or Needles? We will only be walking short trails -no hiking. Staying three days in Moab. What kind of weather can we expect at that time? Also, are Hovenweep and Natural Bridges worth the trip?

Canyonlands is a big, sprawling park as you have discovered. My suggestion is to visit the Island in the Sky area first. I include in this area Dead Horse state park, which views the same terrain. The best view is from Grandview Point. The best short hike is to Upheavel Dome. It is a geological puzzle. I suggest going there while there is still good daylight. We went at dusk and really could not see all that well -- a mistake I hope to rectify in about 7 weeks!!
The road to the Island section is close to the turn to Arches, so if you go to Arches, it is easy to get to that section of Canyonlands. The approach road is also a very spectacular drive.
It should be good weather.
Natural Bridges to me was a fun trip.
We ran up and down the ladders all the way to the creek and stood under the bridges. The route went along ledges, and up and down hill as well.
Some people snort at it, but I thought it was great fun. (I was 56 at the time.) As for Hovenweep, if you see Mesa Verde, you have seen the best. Rather than Hovenweep, invest the time in a drive south on a road from near Natural Bridges to the end of the mesa. There is a view point there that is great. You can see the whole of Monument Valley on a clear day. The road then descends the mesa very steeply.

The northern section of Canyonlands offers fantastic views of the canyon with some short walking trails. We took a 1-2 mile walk in the late afternoon in August watching storm clouds roll in on the horizon--got some great photos. I thought the views were grander in many ways than the Grand Canyon because of the colors, but everyone has their personal opinion.

In May, the days are warm, and the nights are cool. This is especially true of Mesa Verde. You should expect some rain, especially in Mesa Verde. May tends to be the rainiest month. But don't fret too much about it, it still rains less there, than most places on the east and west coasts. Just bring a raincoat, and enjoy. The weather changes quickly, and the suns shines nearly every day.

at islands in the sky, you can walk over mesa arch (short, kinda scary if you're afraid of heights). shafer trail also has great views. you can do this section of the park in a few hours if you don't hike.
ditto on bob's post on dead horse and natural bridges!

I agree -- Canyonlands in some ways is more impressive than the Grand Canyon. I've been all over southern Utah and I think Arches and Canyonlands are my favorites. May is a good time to visit. Not a lot of people, and the weather should be moderate (though it can still get HOT during the middle of the day.)