Emtec kit doesn't fit very well.
Don't know anything about the Bar-Tek one.
Rothe stuff is good, you can buy a full kit from them:
http://www.rothe-motorsport.de/marken/vw/vw_polo_86c_g40.html...or you can get a used turbo from a Passat 1.8t 20v, intercooler of your choice, oil and water lines from a local hydraulics supplier etc. - details on this site tell you what fittings you need. And we (Polo PP) do a range of chips for K03 turbo'd G40s.
PhilJ manifold and downpipe is also an option, in theory the cast Rothe manifold is going to be stronger, but I've not heard of anyone having trouble with one of Phil's steel manifolds.
I went with a Rothe manifold purely because I always intended to run high boost, so with everything getting stinking hot I wanted plenty of strength there.