If you go for the first version, I would definitively make him take ALL the equipment in play, he's a magnet after all, and even if I don't know how they work, it should have the same effect on all equipment.

I think they are both reasonable. In fact it might make an interesting cycle of dudes to print a bunch of variations on the theme.
Lil Magnet Myr 2
Artifact Creature - Myr
At the beginning of each upkeep, choose an Equipment card with the lowest converted mana cost among Equipment in play and attach it to -this-.
1/1
Beeg Magnet Myr 6
Artifact Creature - Myr Cat
When -this- comes into play, attach all Equipment in play to it.
-this- gets +1/+1 for each equipment card attached to it.
3/3
Fuckin' cycles, how do they work?