I have heard people saying that hardwood-floors should always be put alongside windows while others claim it should be put orthogonal to windows.
Which one is the better way now?
The only time I've heard advice about the orientation of the floor relative to the windows is that you want the seams of the floor to lie in the same direction as the predominant sunlight direction. This is so that the sunlight shines ALONG the cracks instead of ACROSS them. It's about making shadows disappear so that the overall appearance looks cleaner.
With that said, unless you are confident in the installation method providing sufficient strength you should install the floor orthogonal to the floor joists regardless of the orientation to the window.
Hardwood floors should be installed orthogonal to the floor joists.
The way I heard it, regardless of your floor joists, you should run the boards parallel to the longer dimension of the space, OR following the path through the main doorway into the space (orthogonal to the wall containing that doorway). This makes the space look bigger because the lines cheat the length and make it look longer.
If that requires you to lay the boards parallel to the joists, then you must beef up the subfloor to at least 3/4" worth of plywood or OSB, and if that's done with more than one layer of plywood/OSB then glue and screw the layers together (make sure the screws go into the joists, pulling everything together into a nice solid substructure).
Lastly, NEVER lay hardwood directly on concrete. ALWAYS lay down a layer of moisture barrier such as Tyvek (NOT a vapor barrier like 6mil plastic; there's a difference), then a plywood or OSB subfloor layer, then your hardwood (possibly with another layer of Tyvek between).
You should by best practice run your flooring orthogonal to the floor joist. You should be able to run it however you want granted that there was a layer of sturdy flooring placed ontop of the base flooring. This adds an extra 3/4 of an inch, and if installed properly, should be layed breaking in the middle of the base flooring giving it more strength. This will allow you to do what you want with your flooring. Your staples for the hard wood will never reach the joist. The sturdy floor will provide plenty to nail to. If there is no strudy flooring then run it with the joist. Be sure to lay your tar paper first before installing your hard wood flooring.