Dinner in Testaccio
Definitely Checchino over Felice, though Felice is not bad either. But if you are going to have one dinner in Testaccio, then Checchino. Go for the Rigatoni Pajata and Coda alla Vaccinara.
L'Arcangelo is terrible. Almost everyone in Rome thinks it is great, but it has declined terribly, so only take advice from those who have been lately. I was there in December and found it terrible and for a long time had everyone against me. Katie Parla just confirmed everything I thought yesterday on her blog.
Never been to Al Moro.
Since we dont have functioning links yet, Ive posted info over on the Restaurants page to reflect the Arcangelo comments here http://www.chow.com/restaurants/915709/larcangelo?tag=search_results;results_list
Katie Parla's review is worth reading
re: jen kalb
Second Checchino and the plates suggested. Its one of the last places to serve truly authentic Roman food. Excellent ingredients, accomodating to tourists, great wine list (and seasonal specials). A cautionary note, the layout is not chi-chic - meaning, it has the feel of an open room taverna vs an upscale restaurant.