Floppy disks are one of the most unreliable storage mediums there are, don't trust those to anything. We don't even have a floppy drive in the house anymore except the old one that came with my laptop 5 years ago and has never been used.
WRT CDR, CDRW, DVDR, DVDRW, the RW's are less stable than the R's but even the R's have been known do deteriorate sometimes. Manufacturer quality makes a big difference there. Search for some of the web pages that compare brands and tell which ones to use and which to not.
I have multiple computers in the house so I bought an USB enclosure and put a DVDRW in it so I can plug into any system and burn. Our laptops can read single layer DVD so even though my writer can do dual layer I only write single layer so they can be read in another system if I should not be able to use the burner for any reason.
Be careful with external HDD's, don't buy a prepackaged one, buy the enclosure and stick your own in it so you know for sure your getting a decent drive, most stick in their poorly selling models to get rid of them. Also remember a rule of thumb for good backup practice is to a different media type and keep it in a different location, another hdd doesn't really qualify since its still the same type of media.