I am currently using an ultrastor 34f, and also have an adaptec 1542c
I used before.  I can generally recommend the Ultrastor as working
fairly well, and it's supposedly real fast, VESA and all that (my SCSI
devices are too slow for me to notice).

I did have to disable the external cache on my machine to avoid
occasionally wedging with the Ultrastor controller.  I get the
impression this is supposed to be the fault of my motherboard's VESA
hardware though (I have a Gateway 2000 4DX2-66V).  Ultrastor sent me a
firmware upgrade which didn't fix the problem (I am still running
fine, just with no external cache, which would probably be a notable
performance hit if I weren't already paging-bound).

The Adaptec 1542C worked fine, but it didn't like the bizarro IBM
Exabyte tape drive I have (the Ultrastor works fine with the Exabyte);
and it's only an ISA card and it WILL NOT WORK with more than 16MB of
memory (this last was the clinching reason I replaced it with the
Ultrastor).

HOWEVER, the Adaptec card is really nicely configurable.  You can do
damn near everything in software; just hit Ctrl-A during booting and
you get this nice little menu.  The Ultrastor card, conversely, is a
real pain in the ass this way.  EVERY single thing you might want to
change is a jumper on the board, and--get this--it doesn't even come
with any extra jumpers so you have to go find some somewhere if the
settings you want have more bits set than the default.  You have to
yank two annoyingly fragile resistor packs to turn off the internal
termination (and not break the pins in case you want to turn it back on).

I have experience with other VESA SCSI controller cards.  But off hand
I would have to recommend any other supported card that is
software-configurable over the Ultrastor 34f.

------------------------------------------------------------------------------