If you're a big fan of fighting games, then you've probably played, and enjoyed both of the games that these two anime are based on. If that's the case then you may well find some enjoyment from seeing your favourite characters fully animated, and kicking ass on the small screen.
The big difference between the two is that the Tekken movie is animated in high-end CGI, whereas the BlazBlue anime is more your run-of-the mill hand drawn animation style, for the most part.
If you're not a fan of these games, then i wouldn't recommend either as they are filled with animation, pacing, directing, character design and plot flaws that can make it almost unwatchable. But diehard fans should at least get a kick out of them!
In the future, the world as we know it is inhabited by humans and Darkstalkers -- beings of the night who descended upon the planet and stole away the light of the sun. Discrimination is at an all time high, fueled by the tendencies of some Darkstalkers to prey upon the humans for their own desires. However, amongst the dark there are those who fight for good, such as the hybrid Donovan and two sisters who are out for revenge. With the coming of the ultimate demon Pyron, the humans and Darkstalkers must band together one last time to save the planet from his wrath...
Both Darkstalkers and Super Street Fighter 4 are anime based on fighting video games. If you want to watch some of your favorite video game characters wail on each other, these are your anime. Darkstalkers is much longer and better in terms of delivering a plot than SSF4, but if you liked one, chances are you might want to check out the other.