[karmoka]

"Je voudrais une pizza" is better translated to "I would like a pizza" "I want a pizza" would be "je veux une pizza"

[idleproc]

"J’aimerais..." is better translated to "I would like...", n'est-ce pas?

[karmoka]

Both "je voudrais" and "j'aimerais" translate to "i would like", albeit with some nuances in the connotations. The later has more of a wishful quality, more open to rejection. In spoken form, they're mostly interchangeables.

[ahoef]

Depends. "Amerais" emphasises the liking of the pizza and "voudrais" emphasises getting the pizza.