I'm visiting Yosemite NP in May. I have about 4 or 5 nights to spend there. I was wondering if I should stay all those days in Yosemite OR stay in Yosemite for 3 nights and stay in Kings Canyon NP for 2 nights. I hear that Kings Canyon NP is quieter than Yosemite, but the scenary is smiliar in both parks, so I am not sure if it's worth the trip. Any suggestion?

Please be aware that the giant sequoias at Sequoia and Kings Canyon National Parks (yes, that's the official designation)
http://www.nps.gov/seki/index.htm
are more impressive and more accessible than those at Yosemite. If big trees are an important part of your trip, Sequoia is almost a given. As for Kings Canyon it's not much less impressive than Yosemite Valley, and a LOT less crowded.

I generally prefer FOR MYSELF to get as much variety in a trip as possible. Others prefer to stay in one place for as long as possible, and get the full impact of that one place. If you are an avid hiker AND can handle the snow that will still be on the trails in May, four to five days in Yosemite will not be too much. But, if you're not into such hikes, that may be too much at that time. In that case, a trip to SeKi is almost mandatory.

I agree with Paul. What do you have planned for Yosemite? It depends on how much hiking you want to do and what will be open at either place. The waterfalls are what to me is the huge attraction at Yosemite. I find the trees in Maripos Grove in Yosemite to be awesome, but the trees in Sequoia area really really awesome. There is fantastic hiking at either place. Wuksachi, in Sequoia, is just typical national park lodging. However, we thought the food there was very good.

I'll be with my dad, so we won't be doing too much hiking. Maybe several short hikes. We'll be there in mid-May, so I wonder if some roads are still closed. How far is Kings and Sequoia NP from Yosemite?

Tioga Road will most likely be closed. Marriposa Grove may or may not be opened. It opened the day we were there last year about May 20th. You will have to walk a long long way if the road is closed to see the trees. Since you don't plan on doing much hiking, you might consider a couple of days at each place. I'm guessing a 3 to 4 hour drive between the two. Mapsonus.com puts it at 2.3 hours. but that was coming from Wawonna, so add an hour if coming from the Valley. You could drive to Hetch Hetchy one day and see the dam. Don't know if your dad could hike The Mist Trail, but it is a nice hike, but is moderate to strenuous and take 4-5 hours.

If Tioga Pass Road is still closed, as is likely, in mid-May and you're not planning a lot of hikes, then I'd make the effort to include Kings Canyon/Sequoia Parks. Much easier access to the big trees.

Sounds like it is likely that I can not go to Tuolumne Meadows in Yosemite in Mid-May?

Here is a link to a site that shows the historical opening dates for Tioga Pass:

http://www.monobasinresearch.org/data/tiogapass.htm

Average opening date is May 29. It might open by mid-May, but I wouldn't count on it. If we have a lot of spring snow, then it will open later.