just wondering, by activity do you mean urban development, shops/retail or foot traffic?
if you mean max specifically, westside max has tons of new apartments within walking distance of almost all the stations (west of beaverton). they are too numerous to name. within portland there are many particularly around goose hollow, pge park stations, and along the burnside stations on east side max. not a whole lot of very close apartments however along the I-84 stations, the core of downtown or in the lloyd (although there is 'the merrick').
there are tons of apartments along the streetcar line (like NW Portland, riverplace, psu/south auditorium area, pearl) and even more along the major bus lines serving the inner east side.
perhaps your best bet would be to use windows live local
in birds eye view following the max line to see if an area looks good and we can work from there.