i like the Deutsch connectors as well. just make sure you have a quality tool to crimp them with.
as has also been stated, sometimes you need to use an un-insulated spade, ring, or pin. i like to use the ones that are tin plated, but i have also used bare copper as well.
when using shrink tubing, i have now started to use the marine grade, which has a sealer glue inside. just seems like an extra measure of keeping a good connection between the wire and the terminal.