String or tuple and unions

[Grumfish]

Which is faster to read from, a string or a tuple? All items would be
1 unicode character and I would be mostly treating the string as a
tuple, only looking for items.

Two more questions, is there a way to find the union of two sets? And
how fast does the len() function work? Would it be worth my while to
store the length of a large string (or tuple) instad of using len
several times?