Another factor you should consider is the looks, if that even matters to you? Only the low offset ( either +15 or +22) real Volk TE37 comes in the concave faces ,which in my opinion makes any car its on look alot more aggressive. If you get the offset any higher then that then the faces are going to look flat, which is a less desirable aspect to some people (me included).
To me, I think the best TE37 combo for the mk3s is 18x9.5 +22 and 18x10.5 +22, but that's just me. Or if you're gonna run some big brakes in the fronts then 18x9.5 +15 would be the way to go for the fronts.
Also if you're planning on buying brand new, these rims cost about $3600-4200 since now the dollar sucks and the yen has gone up considerably.