As Steve: said, the BEST route to go is one that has the least amount of 'height' associated with it. And yes, the flexible ducting is the WORST because of its corrigation. It tends to bind the lint. In short, go up as little as possible and directly out the wall to the outside. It's OK to cut a hole in the ribbon joist (that's the size of the duct) so you can get outside.
Now, the question is: What do you have for an outside wall??? If it's brick, you might want to hire a Pro to at least cut and finish off the hole. (A brick mason would be best.) As far as running the ductwork, do your best to install it with the LEAST amount of 'turns' in the piping. The more turns you have, the more 'likely' lint will collect.
I would not vent your dryer into a crawlspace or into the basement, itself. A dryer pushes a LOT of heat over very wet clothes and that moisture will only cause problems. If vented into a crawl, it will condense out onto wood joists and subflooring, thus causing dry rot. If vented into the house, you'll end up with a HUGE humidity level and nothing but mold and mildew. There are these 'gizzmos' that are sold that 'permit' you to vent into the house or crawl but I wouldn't do it. (The next thing you know you'll be wondering why you have that strange 'smell' in your house!)