Well as you can see there is no perfect answer as there are many solutions but the real challenge here is understanding exactly what each device can do or not do.
Just some thoughts -
PS3 - if the type of files you have already work on a PS3, then it is a great choice. Caveat for PS3 is that it is limited in what files it can play and some sadly are very common formats that Sony opts not to support. - MKV comes to mind. There are ways however to convert some files to formats that the PS3 can play from your NAS. PS3 will not support some HD Audio such as DTS-Master within a file from your NAS. You may get the image but no audio. Again, always make sure you know what is supported by the device.
Blu Ray players - similar situation in that some offer more bells and whistles than others including streaming options (Netflix, Amazon, Vudu etc.) along with access to locally stored media files (via USB directly or through your home network to a NAS). Always check to see what file formats are playable from the USB storage and the NAS - they are not always the same.
Some players state they support DLNA and also some can see network storage without DLNA.
NAS - Short and simple - always make sure you set up the software within that handles DLNA. Items to pay particular attention to is "permissions" and identifying where on the NAS your media files are stored. While some DLNA software can convert files for you, it usually is a bad show (figuratively and literally) and highly suggest that you play back files that are already playable by your Blu Ray player. NAS should never be considered a "back up" solution* However, a properly cared for NAS may have over time its challenges but usually can be resolved (drive failures or power supply etc.).
Yes to the port - As silly as it sounds, some people run into problems because they might have more than one device connected to their TV or receiver etc. and fail to tell the TV or receiver to switch to that port. Example being HDMI input 1 on the TV might be for a cable box and HDMI input 2 for your Blu Ray player. You can't get Blu Ray to show up unless you tell the TV to go to input 2 (don't laugh but I see this way too often with some of my friends). The same applies (and more so) with connecting the above to a receiver (AVR).
Hope the above is considered food for thought and useful.