Depends entirely on your budget really mate.
Miltek kit is great, you really can't go wrong with it at all.
However, if you want to save some money, it's possible to get a high quality stainless steel turbo back system for just £260, all brand new! Providing you can do the labour yourself, and have access to a welder
I decided to give some cheap products a try, and got incredibly good results.
Rather than spending £400 on a miltek sportscat and downpipe, I spent £100 on an ebay 3'' DP and decat, which flows equally as well as a miltek anyday, but won't pass an emissions test. I think that's worth it to save £300 though.
Then, for the catback system, I took a gamble on the toyosports 2.5'' catback system on ebay, for just £140. This needed modifying though, with the front section chopping off and replacing with a 2.5'' length of pipe to mate to the decat. The length of pipe cost £20.
That little lot came to £260 in total, and I'm really happy with it. It fits great, I like how it looks, and it's got a nice noise to it without being loud at all.
Not suggesting it's for everyone, but it's an option, that's worked very well for me with a bit of lateral thinking