I think 那个饭店既便宜又好吃.（better） 1. We usually say 既（ji）......又......not又......又......in a sentence. 2.Before we had been to another restaurant, this time you can use a “也”. This is a comparison.

If you are using 又 to mean "again", then the starting point of understanding 又 is the start of your conversation if everything has happened once and you are talking about another time something happened, then you can use 又 example 我星期一去了上班，星期二又去了上班。(With 又, you need a 了 after the verb) In your question, you are using 又 to mean also, also, etc ... 又。。。又 also ... also 那家饭馆的菜又好吃，又便宜，又方便，又健康。 in your second example 也 means and or also ... and you would only need one 也 to link two verb phrases ... wtih 也, both of the verb phrases must have the same subject ... 那个饭馆的饭便宜也好吃。

那个饭馆的饭也便宜也好吃。 <= wrong

那家饭店的食物既便宜又好吃

那个饭馆的饭又便宜又好吃。