They both had upsides and downsides.
I loved Slizers figures for the use of now-rare element colors, the multitude of gear functions, and the outlandish designs of their characters.
I love the Hero Factory sets for the versatility of the components, something that the rather restricted Slizer bodies and other gimmick-pieces just don't have*, and the poseable skeletons introduced with 2.0.
As for the stories, Hero Factory actually has one, albeit one that does not interest me in the slightest, whereas Slizers had a disappointingly small amount of Story, though I liked the esoteric and vague feel of the little tidbits given in the Slizer construction manuals. Neither one influences my opinions on the sets to the degree it did with BIONICLE, so it matters little.
*This is why HF 3.0 was a horrible disappointment to me. It combined a lack of gimmicks with an array of new pieces which were quite difficult to use outside of their original purpose; the only reason I had to buy those sets was for recolors of pieces introduced in 2.0, like gold snap-on armor. At least I was able to use Rocka's lion head as a pauldron on a Rocka revamp I made. I need to upload that sometime.
Edited by Bominominomu Nemo, Dec 02 2013 - 12:27 PM.