It's hard to beat steel as the most accurate trainer (though even the blunts don't behave exactly the same as sharps in the bind), however good steel trainers are expensive, and there are still safety considerations.
Cheaper alternatives have historically also been less safe, namely wooden wasters and aluminum trainers. Both of these suffer from having almost no give, so injuries are more common if these are used for full-speed bouting. Realistically, these should only be used for controlled drills.
Most synthetic/plastic trainers to date have had problems with having poor weight and balance, even though the softer flex makes them safer. Purple Heart came out with a pretty decent one several years ago, which were used as the official tournament swords at Longpoint last year.
However since then, Purple Heart has come out with their "Type 3" model, which seems even better. It looks like some of the HEMA competitions have switched to these.
http://www.woodenswords.com/ProductDetails.asp?ProductCode=TYPE-IIII haven't had a chance to put it through its paces yet, but I ordered one and received it last week. The weight and balance are very realistic. The blade has flex, but not too much, and appears to be CNC milled out of a solid piece of plastic. The guard and pommel are steel, and I think it has a metal rod or tang inside the grip to keep the hilt from flexing. The blade has both a profile and a slight distal taper, but has a nice wide thrusting tip.
At $125.00 for a longsword, I think we may have found a better inexpensive alternative.
