I've done one of Revell's 1/144 Type VIID Minenleger models and that was a good kit, not too difficult, a good size, and looked great once built. Plus I got it at half price from my local model shop

There's also a few aftermarket detail parts for it too, which I actually didn't bother with as I thought it looked fine as it was, but the option is there. The only dissapointment for me was that I couldn't find any 1/144 scale crew for it anywhere, you can get 1/72, 1/32, even bleeding 1/300! But anyway, yeah it was a great kit, as are their other U-Boats I believe.