It all depends on how much money you wanna spend along with what your preferences are with regards to sound (which I'd suggest researching via YouTube to decide that).
With money as no object it's generally agreed that the pecking order goes corsa>borla>magnaflow>flowmaster>....
IMO, once you get down to Magnaflow and Flowmaster and below it's mostly a preference in what sound you want. I LOVE flowmaster and it's sound and have had them on several vehicles with very good luck. With the Burb I went with a Magnaflow mostly because I'd never had it before and just wanted to try something new this time. I have been very pleased with it and it's giving me the sound I was looking for with it. If you're just going to replace your muffler but keep everything else intact (like I've done as have many people here on TYF) I'd personally go with either a Magnaflow or Flowmaster (or the like) because they are reasonably priced. With the Corsa or Borla you get the most out of them when you get their catback system and get the sound
and performance gains and they are also MUCH more expensive 99% of the time. Does that make sense?
This is just my 2 cents worth and I'm sure there will be differing views but that's based on my experiences and research