Only done 100 easy going miles in the rebuilt 1.9 engine so far, so hard to tell yet as taking it easy for the minute.
The 2.1 I'd say was gruntier with a bit more poke (unknown s/h condition engine I had put in about 8 - 9 years ago).
My original 1.9 was knackered when I bought it (soldiered on for about 2 years) - my baptism of fire into (the then) unknown world of VW's - was a Moggy 1000 / SAAB man so VW's were an unknown quantity back then
My new 1.9 was rebuilt from scratch by a VW guy "Tudor" down West Wales - loads of local VW guys swear by his rebuilds.