Whilst technically Lionheart is the better of the two (Beast), Beast would get my vote for the end result. In 1989 Beast was a remarkable looking and moving game. Ok, the gameplay was a bit suspect, but as a demonstration of what the Amiga was capable of, Beast was responsible for selling more Amigas than Commodores lame TV adverts.
4 years later, Lionheart arrives. Whilst technically its very nice with its 1pixel parallax scroll, vibrant copper bars and nice graphics, it has problems.
The graphics look too flat because the copper fade underneath is too bright, making the graphics stand out too much. The sprite is nicely animated, but ultimately its too small to be detailed enough.
The music is nice, but then again, Beasts wasn't exactly crap either.
Thalion was the problem. They simply didn't have the funds to successfully market the game properly. Lionheart was a good enough looking game that Ocean or Psygnosis would have wanted to translate that to the SNES and the Megadrive. And in the case of the Megadrive, it would have showed just how much better the Amiga was in the graphics department, because the Megadrive simply wouldn't be able to compete with only 64 colours onscreen from its pallete of 512.
Fact is, Thalion were utterly incapable of distributing their games effectively. Rainbow Arts realised very early on that for them to succeed beyond their own country, they would have to have distribution partners in other countries, which is why they were so prolific. And this being a company that were branded as cheats by some because they didn't pay early developers properly!
No Second Prize was another great game by Thalion, very fast, quite detailed and all on an Amiga A5oo, but because they had such crap distribution, their good games never sold in as many volumes as they should.
Lionheart was too little too late. If it was a year earlier and with Ocean, Microprose or Psygnosis distributing it, it would have been a huge hit and then converted to other formats.
As it is, considering it had 4 years potential development skill from the time that Beast got released, it wasn't as good as it could be.