Lightbox popout styled like this:
Or a non-popout with the slider:
Which is the most effective/easiest to use, etc? I am creating a website with photos from robotics competitions.
There is no 'best' gallery method, it all depends on your site. It's like asking what the 'best' colour is - it depends on the design, your preferences, intended audience, etc.
Lightbox would probably be easiest to implement as you just have the thumbnails and the lightboxed version of each image. With the second one you have the thumbnail, the main images and the slider. The slider will add complexity.
As the designer/developer only you can decide which one is 'best' for your site