I've been searching for "the" e-commerce extension for a while, and I've tried all the major "players" (with an idea that e-commerce just has to be "hard and for hard-core developers only"), prior to stumbling on Hikashop.
It INSTALLS in a snap. It WORKS! and it works circles around other extensions, in my opinion.
It's very easy to set up all the various aspects (shipping, payment, etc.) compared to what I've had to deal with elsewhere.
Now the best yet, is SUPPORT. These guys are not kidding - top-notch support, going into DETAIL in answering my questions, and FAST! I'm still in amazement from having looked at my email this morning to find all my questions fully answered, and with a smile :)
I highly recommend this shopping cart to anyone that is after quality, speed and no headaches :)
Thank you, Hikari Software Team!