Ever go to a place and see a little card and pencil with a column each for Nigiri and Maki, with individual fish listed and a quantity line next to it? There you mark down what you want and how many pieces each. Fill out like three of them and submit them to your server after you've got your drinks settled, and you should get them pretty quick. If they don't have these cards, you may not get your order quickly.
Sometimes it's hit or miss; check the reviews online first. Back where I grew up in Florida there was a place where you'd get your order in less than two minutes, but the quality wasn't very good.
For an 'authentic experience', you want a simple place with an old japanese guy or two behind a bar watching a baseball game on a tiny tube TV, possibly with some shouting going on. This is super rare in the US from my perspective, but I have found a few places like this in south florida, so you may have luck elsewhere too.
For just a 'good sushi' experience, you want either a japanese convenience store that makes sushi to order, a super pretentious expensive place pretending to be a high end sushi/sake bar, or a place that randomly has a really well trained chef that imports really quality ingredients [which is typically only pretentious expensive places]. Food blogs are a good resource, though they can often be more pretentious than the restaurants.
I like to try out new places and order either chirashi or whatever the chef's nigiri special is, maybe with tuna or beef tataki beforehand to see their prep skills. Most places that don't have japanese chefs fuck up the tataki, and you can usually predict the rest of the quality from there. If you don't get paper thin slices or they come back over-seared, your sushi is gonna be sub-par.
Note: the best sushi i've ever eaten in my life was last year at the now-closed Barracuda in the Castro, so don't overthink it, just order some nigiri and see what happens.
All those places pale in comparison to some of the best sushi (IMO) in town though, if you're willing to spend quite a bit more. Check out Kusakabe in the Financial District :)
To be fair, I haven't been to every sushi place in the city (or even every sushi place in the Castro), so maybe you can find worse places, but overall I was just very disappointed with Barracuda.
> Every piece I tasted was like a totally different animal
Assuming that you were getting different types of fish with each piece, then I certainly hope they tasted different! If the sushi restaurant you're eating at serves up different fish and they all taste the same (or, god forbid, they all "taste like fish") then that's not a very good sushi restaurant.