Working with HikaShop is a pleasure. The best way to say it is that it just works. Out of the both not only does it work great, it also looks great. It is also highly customizable, and quite easily so. All customization can be done right through the admin interface including template overrides.
I can't recommend this shopping cart enough. If you want a no nonsense shopping cart that works exactly as it should, with fantastic support and documentation, look no further than HikaShop.