Plenty of Fish is available to those who reside in the United States, Canada, UK, Australia, France, Germany, Ireland, New Zealand and Spain. Plenty of Fish offers paid and free upgrade memberships.
The website offers Android and IPhone apps and draws web savvy singles.
With OK Cupid you can send a number of questions a match must answer before communication begins.
Like I said, level of activity is related to your success to find a match on OK Cupid.
Date Hook Up competes with OK Cupid mainly because it appeals to younger singles and university students.
One thing that sets Spark apart is your ability to send and reply to emails if you are not a paid member.