Source: http://hearthstats.net/apr

Hearthstats has released their aggregated Statistics from April 2014 for both Arena and Constructed. The top three most played classes for each play mode are as follows:

투기장
1. Mage
2. Paladin
3. Druid

등급전
1. Warlock
2. Hunter
3. Druid

In terms of win rate, the classes ranked as follows:

투기장
1. 마법사 53.20% (50882 Games)
2. 도적 53.11% (23518 Games)
3. 성기사 51.69% (36685 Games)
4. 주술사 51.54% (26950 Games)
5. 드루이드 49.33% (31931 Games)
6. 사냥꾼 47.14% (22417 Games)
7. 전사  46.24% (14642 Games)
8. 사제 42.25% (15710 Games)
9. 흑마법사  42.21% (11051 Games)

등급전
1. 흑마법사 52.38% (88921 Games)
2. 드루이드 51.01% (61290 Games)
3. 사냥꾼 50.60% (77223 Games)
4. 주술사 50.33% (34309 Games)
5. 전사 49.94% (40803 Games)
6. 도적 48.60% (33923 Games)
7. 성기사 48.24% (27321 Games)
8. 마법사 47.82% (39035 Games)
9. 사제 43.99% (28059 Games)

Keep in mind that these stats are taking from a variety of skill levels and do not necessarily represent top tier play. Make sure you check out Hearthstats for more detailed matchup statistics