I can't tell you scientifically, but I've taken ampicillin, which has the same, a little bit milder side effects than amoxicillin. and I've also taken cefixime, and cefixime had NO side effects on me whatsoever. and it worked well. ampicillin made me feel mentally confused and tired and darn nauseous.
so if you're wondering what to take - i wouldn't give it a thought - would take cefixime over amoxicillin any day, because after all they both work on the same (wide) range of bacteria!