Umm good question, I think a historically accurate sharp is what I really want. I for some reason seem drawn to that option.
Ok, well with sharps the brands recommended by James are spot on. The difference between a $900 sword and a $500 sword usually comes down to subtle geometry. The $900+ sword will feel and behave like the period original swords that companies like Albion and A&A spent years studying, measuring and handling. One common thing people like to point out (myself included) is that most expensive swords include distal taper. That is a sword is thicker at the shoulders of the blade than at the tip. It's hard to pull off, and requires a steady hand, good technique, and a high level of skill. That's why cheaper blade makers skip it. The result of doing it properly though is a lively blade, balanced properly, and without the feeling of being overly blade heavy. Profile taper on the other hand is a lot easier and is a function of the type of sword and style of blade.
For materials, a proper sword is made from carbon steel, never stainless. Stainless steel is incredibly hard, and in lengths longer than a knife is prone to breakage. A stainless steel sword can crack or shatter when struck against something (and of course stainless steel is not medieval in any way). Carbon steel on the other hand is hardened and tempered. Hardening the steel makes it rigid and allows it to retain its edge, but makes it brittle. After the steel is heated and quenched it is effectively hardened by realigning the crystalline structure of the steel at a microscopic level. But this is too hard and brittle for a sword. It is then tempered. It is heated to a lower temperature and allowed to cool slowly. This allows the stresses created by the hardening process to ease. The result is a blade that is quite hard, yet springy and soft enough to prevent breakage, while simultaneously not being too soft that they easily bend and stay that way (i.e. "take a set"). This is desirable in a sword and is necessary for a sword to be functional. So avoid people selling 'stainless steel' swords, they're just dangerous SLOs (sword-like objects).
And finally on this little sword primer, swords are as varied in shape and style as modern firearms. The differences may be lost on someone without a trained eye, but they are there. A viking sword has a flat lenticular cross section, and really not much of a tip. It's awesome for cutting. A late medieval longsword may have no fuller (the groove in many sword blades that has
nothing to do with allowing an opponent to bleed btw, they'll bleed just fine without one), and have a diamond shaped cross section, be relatively rigid, and have a awl-like acute point optimized for the thrust against an opponent in armor. To get an idea on the difference between sword types you'll want to familiarize yourself with something called
Oakeshott Typology. Ewart Oakeshott was a historian who came up with a now commonly used classification method for medieval sword blade types.
Another great resource (but not infallible) is the Albion Europe site. You can browse the different sword models they offer (mostly identical to the US offerings). But they have little timelines under them that show you when a particular style of sword is appropriate! It's a good quick reference, but should ultimately be checked against period resources. Of course different types of swords within the same period may be used by different types of soldiers as well, so always check if that's a concern!
http://www.albion-europe.com/swords/swords-by-time-period/medieval.aspxHere you can see the difference between distal taper and profile taper on a knife. The same applies to a sword:
