What is the best index for this query??

[hrg wea]

I have the following table:

create table comment(
	id int not null auto_increment ,
	userId int not null ,
	content text ,
	timeStamp int not null ,
	primary key(id)
) ;

And the following query:

SELECT * FROM comment WHERE userId = 10 and timeStamp < 11981234 ORDER BY timeStamp DESC

What is the best index to use so this query is performed the fastest way posible??

I think of two possibilities:

The first one:

index(userId,timeStamp)

and the second one:

index(userId),
index(timeStamp)

which option is the best for this query and why??

Thanks in advance.