a lot of brands each offer different kinds of mufflers...
for example, magnaflow makes both chambered mufflers and straight through mufflers, they are mostly known for the straight through type... while flowmaster are mostly know for chambered mufflers. shorter mufflers from any brand will be louder and longer and larger mufflers will tend to me more quieter.
bottom line is that I would start by listen to as many sound clips as possible to see what kind of sound you are looking for. for me, I was really loving how my flowmasters sounded (40 delta flow) but an excited to get the new single center muffler set up on it soon.
tip are all about looks, if you are going to do new tips, have it down at the same time as the mufflers. with the original flowmaster setup, I reused the OEM tips, however with the new magnaflow setup I also grabbed some larger rolled edge angle cut tips that were power coated black.