Few questions about selendroid and appium

I have gone through many blogs and tutorial on net to find out which is best tool to use for android & ios app. However, I came across selendroid and appium are widely used tool for mobile app automation. I have gone through multiple blogs and tutorial site and found information which are outdated older than 2015. Now, I want to know that

1. Which one is best among this two?
2. Does selendroid and appium test script can run on android and ios app without any change?
3. Advantage and disadvantage for this tools?
4. Do we have any other open source tools which are better than selendroid and appium?

I would appreciate your inputs...

Answer to your questions:

• If your are planning to use it for both iOS and android, i would suggest to go for Appium.
• Yes, if your locators and app structure is same then you can use same script on both platforms.

Appium- Advantages:

• You can run test parallel
• Same scripts for both platforms is possible
• Doesn't require access to your source code so you are actually shipping what you are testing
• Good documentation and various blogs
• Support for various framework
• You can write test in your favorite language

Disadvantage

• Doesn't support image comparison

I have been using it for 3 months. This is what i have figured in 3 months.