Rocks and dorks are more efficient and provide value earlier than land ramp. I think it's more a matter of synergy for your deck. Do you particularly want more lands in play and are in green? Run land ramp. In most cases though the 1 CMC dork is still better anyway in green as you're likely playing a creature deck with cards like beast whisperer.

Removal happens in commander but how frequently is someone actually packing that much dedicated artifact removal that you're worried about someone blowing up your arcane signet? As a control player myself it's just not an efficient use of my mana most of the time unless I'm clearing multiple artifacts at once or if you kept a greedy hand with incorrect colours. I would rather destroy the 5cmc bomb you played the following turn if it's that big a hindrance as all I have done is maybe put you back a turn whilst wasting a precious card that could have been better used later. Signets provide good value quickly and don't cause such a massive loss in tempo that land ramp does.