I run an Oade Mod R-44 with a variety of pres in front of it, including the USBpre2 which is probably my favorite. Although it is plastic, I find it to be very rugged feeling. I also find it to be highly reliable, and the footprint is small. I've even "stealthed" with it (where a door search wasn't involved).
I'm not really sure anything was wrong with the stock pres and I have great pulls with both. I don't always run an external pre and am happy not to when I want a smaller gear bag.
The Tascam I have not used, but things that are obviously true about it are:
-- It is significantly larger
-- It is made by Tascam
-- It has 4 more channels
I'd love to have a compact 8-channel deck, but to me, for the rare times I'd need that, the -44 + syncing with the USBPre2 to a second deck is about as good an option, and means my bag is lighter the other 95% of the time I don't need more than 8 channels.