I THINK, BVA...

ECP

ans is BVA because in login screen(web),the tester will 
test user name and password  field ranges only. user name 
and password will accept the all special charectors 
numerical,  and alphanumerical.(insted of  space)

a)	In login page both (BAV and equivalent partition   
class) are used 
b)	BAV is nothing but what is the length of the that 
object
c)	Equivalent partition class is nothing but valued 
data set.
d)	In login page must and should be apply the both 
tests
e)	If not the both test that is not login page test 
not completed.

for login screen :
input domain test :
length check(bva)+valid check (ecp)
both are doing for login screen

If u do Boundary only then u hv Covered all the Partition 
also but it is not vice-versa.

Technique we choose depends on the requirements , here in 
case of login screen for a web page we use  EP , 
for eg : if the username should be 5 charc long , then we 
can go for two invalid and valid conditon , by guessing if  
all these conditions are passed then we can assume 
remaining value will be passed .

For the Login screen We can apply both BVA and Equalance 
Partion.

If the username and password are in specified value there 
we can apply partiion the data ateast one valid and two 
invalid data,
If it is in the specified range we can apply the bva ,we 
observe the lower and upper boundary limits