Others can give you more details about the many different options for flats that are available, but I can tell you a bit about the Thomastik-Infeld flats, as I have them on all my basses, two 4 strings and a brand new 5 string. I think you would find these TI strings to be very vintage sounding, and from what I've read, can almost literally last forever. I love these strings for several reasons. First off, they are pure nickel wound strings, which I believe gives you the warmest sound. Secondly, different strings require different amounts of tension in order to get to the correct pitch. TIs tend to be lower tension than most. Some people like that, others do not. I happen to love that fact about them. Lastly, they are probably the most expensive strings out there. I think the price is about $105 for a set of their 34" scale length for a 5 string set. But well worth the price, IMHO!!