All of the above are correct. From the grammar point, all of the sentences omit the object 我. So they should be 我很高兴见到你 (wǒ hěn gāoxìng jiàndào nǐ) 我很高兴认识你 (wǒ hěn gāoxìng rènshì nǐ) or 认识你我很高兴(rènshì nǐ wǒ hěn gāoxìng). As for the last sentence, 认识你 becomes the topic, making an emphasis on the context. I hope my explanation helps! :-)