which option should i use for ads in youtube ?

Monetize with Ads Ad Formats

Overlay in-video ads
TrueView in-stream ads
This video contains a paid product placement
Display ads are shown by default.


Syndication

Everywhere

• make this video available on all platforms

Monetized platforms make this video available only on monetized platforms

It's not a very difficult choice, just check all of them and allow on all devices.
Unless you absolutely want to be picky. Try the Overlay by itself incase your visitors get tired of waiting 30 seconds for ads.

For me TruView in-stream Ads works better then Overlay (If you are asking for best conversions)
Make it available on all platforms (Even if it's not monetized, you'll get views, that'll help in ranking of your video)

Doesn't really have much of an impact, just select all of them like funky suggested.