It's Yoshi's Island 1. The big bullet bill at the start is the big opening set piece. It's the Orca from Sonic Adventure. You get your feet wet, before they introduce the shiny new game mechanic in Yoshi in the second level.

Yoshi Island 2 (despite the name). It starts displaying the goombas and koopas as the first enemies and it reinforces the idea of using its shells to kill the conga line...

I always start by going to the right to "Yoshi's Island 2". I get that it's not optimal, but it just makes the most sense to me for some reason. I also think that it serves as a better intro to the game than "Yoshi's Island 1".

I feel like statistically the answer might be Yoshi’s Island 2 since people choose to go right more often when given the choice, but at the same time it is listed as the 2nd level and the Gamer’s Instinct might take over and make people switch to level 1.

Mario games always have you run to the right, so I go right first.

Yoshi's Island 2, you go right first.

You’re all wrong, it’s the intro text screen. Especially if it’s a Kaizo intro screen.

@bollard: @noboners: Yes, in Mario games you go to the right. However, going right means you start at the left and then move to the right. It's more accurate to say you go from left to right. We also read from left to right. When you open a book, you read the page on the left first.

I say it's stage 2, getting Yoshi really feels like Mario World has "started" since stage 1 has a fire flower at best which is found in any other game. For instance, Mario 3's stage 1 has the Tanuki leaf and you're able to do the thing that sets Mario 3 apart.

Also, to expand on earlier comments, I think you're naturally going to go to the right on the world map cuz there's the castle and other things that stand out to the right. That's just my thinking and not based on any real science.