Best Asian food in Boston.
By 'Chinese' you probably mean Americanese. You should try some of the local Sichuan places. We have some really great ones. "Sichuan Gourmet" is the best in terms of heat and spice. For raw heat I like their 'JinGu' fish, but they make a lot of other fiery dishes. Apparently the Billerica location makes the hottest food, but their other locations make food that is more flavorful, while still being fairly hot.
"Chilli Garden" in Medford does excellent work and has many spicy but not hot dishes. Sichuan Garden II in Woburn is also a favorite of mine. "Red Pepper" in Framingham has a lot of things you won't find at the other places, and is decently hot. Other Sichuan places I've enjoyed (despite their names) are "New Shanghai" and "Thailand Cafe".
I'm very surprised nobody has mentioned Phien's Kitchen in Lowell. They're Laotian and will make food plenty hot--their papaya salad was almost too hot for me, and too hot for my DC Andy Tannenbaum. They said they can make their other dishes comparable in heat to the papaya salad.
But if you want *REALLY* hot and authentic food, go to DC, to a place called Bangkok Golden 3 in Seven Corners, ask for Chef Seng (also Laotian) and tell her a guy from Boston sent you. She'll make some food that's way too hot for even you to eat.
586 Westford St, Lowell, MA 01851
Just fyi, you're looking for "southeast Asian" food. That'll focus it on Thai, Vietnames, Cambodian, and Malaysian.
I like Xinh Xinh (Vietnamese), Thmor Da (Cambodian in Revere), Rod Dee in Cambridge, Dok Bua, and Pad Thai Cafe (last three are Thai). I haven't had a chance to try the Vietnamese places in Dorchester or some of the other Allston-area Thai places which I gather are also very good.
Further afield, there are good places in Lynn and Lowell.
Dokbua Thai Restaurant
411 Harvard St, Brookline, MA 02446
7 Beach St, Boston, MA 02111
Pad Thai Cafe
1116 Boylston St, Boston, MA 02215
1906 Massachusetts Ave, Cambridge, MA