Agree with the above posters.
It really depends on your personality and your ability to follow up. If it was me, I wouldn't be able to stand the thought that the cancer is lurking in my blood just waiting to come back (especially since you have a component of embyonal and chorio - one a lurker of the blood and the other aggressive). Of course, only time would be able to tell if any of the cancer is in your blood but, with embryonal it's much more likely then with teratoma or yolk sac. Plus, embryonal is extremely sensitive to chemo!
Chemo sucks, no matter what. No one is going to tell you it's a walk in the park but, it's probably better to get any remaining cancer cells now compared to if they seed any organ/lymph nodes.
Just make sure you do sperm banking before starting chemo (hopefully you didn't end up with retrograde ejaculation after the surgery or you already did sperm banking). You are so young and even though you may not want kids now, you may in the future and chemo could leave you infertile (30% chance).
Good luck, it's not an easy decision but make sure you do lots of reading and ask lots of questions.
1/15/2010 - diagnosed with testicular mass (2.5x2cm): 2cmx2cm para-aortic lymph node on CT scan (no other abnormalities)
1/19/10 - R I/O
1/21/10 - path results back Embryonal carcinoma 95%, teratoma 2%, seminoma 2%, and yolk sac tumor 1%
2/1/10-end of March - 3xBEP
4/7/10 - CT chest/abd/pelvis - lymph node normal, no new masses
all of 2011- all labs and imaging normal
--> still on surveillance