Layman will have fewer PP and more limited access to spells than Alchemists, so it's mostly a question of how productive you want them to be. Also, even at lower levels the alchemy spell lists are going to grant crafting bonuses, so with their low PP you might have Laymen who are spending a fair amount of time just making conventional things, with only the occasional magic item. Do you want a lot of minor items being bought and sold? Alchemist might make more sense. Are they supposed to be uncommon? Layman.