I have an A-Designs Red and Blue unit in my lunchbox, and recently added a DIY Fivefish Studios SC-1mk500 pre.
The A-Designs Red and Blue units are both transformer in/out, where the FiveFish is transformer in only.
The Red is very mid-forward with a super tight low end, with a tame top end. It sounds awesome on stuff like guitars and toms and even snare. It also does well on acoustic guitar.
The Blue has a high-end glassiness that I like when paired with a darker mic like an SM7
or a 57. Paired with a LDC, it sounds great, but sometimes has a higher-end harshness.
Both the A-D pres have around 65dB of gain. They are SUPER QUIET.
The FiveFish pre has seen limited use so far, but it sounds awesome on the stuff I've tried it on - electric guitar, acoustic guitar, and vocals. It has a similar mid-forward character (due to the input tranny) as the A-D Red, but it has a nicer high-end gloss. The lows aren't as tight - maybe a little sloppy - but for the sources I've tried it on, it represents an incredible value. It lacks some of the build quality of the A-D pres (I built the darn thing after all, crappy solders and all), but once it's in the lunchbox who cares?
The A-Ds go for around $700 while the FiveFish retails for $299 without the tranny/$360 with. While I love my A-Ds, I will probably buy another SC-1mk500 just to have a nice stereo pair.