I love the look of white string lights but if the venue doesn’t include them, they’ll be expensive to rent (and have put up), or might not allow them. On the positive side, uplights are cheap to rent and easy to set up.
Up lighting is going to give you a lot more bang for your buck. They can set colors to evoke an entire mood in the room. It can be subtle (peachy rosey colors) or a wow factor (blue, purple, turquoise). I actually had a package that included both café lights and uplighting