Personally, I'd go with 4.

But, your choice should depend on the variety in the other salads' ingredients - ie: if your potato salad has meat and a mayo or cream based dressing, then go for a vegie or non mayo dressed version of the pasta salad. If both the rice salad and potato salad have capsicum in them (for example), then I'd made a version of the pasta salad with no capsicum.

Another option to throw a spanner in the works with: I do a pasta salad with baby spinach, spring (green) onions, blanched green beans, cucumber, cherry tomatoes, crumbled feta and crispy grilled or fried salami or prosciutto. Lemon juice, olive oil, sea salt and black pepper for dressing. Sometimes I also put in black olives (especially marinated ones). Really easy, and very flash looking too.