I have used Spelling City for a couple of years. I used only the free version until this year. I think there were enough options available on the free version to satisfy most students.
This year I decided to take the plunge and buy a subscription to Spelling City because I have three spelling groups, a below grade, at grade, and an advanced group. The subscription helps me track assignments and tests.
The only bad part is that I give Challenge words that add to the score, but don't penalize students that miss them. The scoring on the site wasn't working to my satisfaction, so I have students take the spelling test online, print it, and then add the challenge words. I just look over the challenge words when I go to record scores. I love that I don't have to decipher illegible writing. Most of the grading is done for me. Students like the game format for studying words. Parents like it, too. I think the cost ($49.99) for a classroom of twenty-five students is worth it. Keep your eye open, as they offered a sale in August this year, for 33% off.
I also decided to alter my spelling contract to reflect the additional Spelling City activities for students. I am including it for any that are interested.