Here's the character popularity poll from DB Forever, which should give an idea of each characters' popularity among Japanese fans around 2004-2005. I think "points" refers to how many people identified each character as their particular favorite, but I'm not sure.
1. Goku: 6,235 points
2. Vegeta: 2,527 points
3. Gohan: 2,131 points
4. Trunks: 1,487 points
5. Piccolo: 1,176 points
6. Goten: 798 points
7. Kuririn: 736 points
8. Boo: 421 points
9. Freeza: 324 points
10. No.18: 204 points
11. Mister Satan: 201 points
12. Karin: 185 points
13. Kame-sennin: 172 points
14. Cell: 170 points
15. Yamcha: 163 points
16. Tenshinhan: 125 points
17. Bulma: 112 points
18.No.17: 98 points
19. Yajirobe: 93 points
20. Videl: 86 points
There were also at least two popularity polls that ran during DB's serialization in Jump. One was in Weekly Jump issue #12 for 1993, the same issue of Jump with chapter 411 (the one where Cell self-destructs). The results were:
1. Gohan
2. Goku
3. Trunks
4. Vegeta
5. Piccolo
Another ran in Weekly Jump #05/06 for 1995, the issue with chapter 501 (Gotenks-absorbed Boo beating up on Gohan), and the results were:
1. Goku
2. Vegeta
3. Trunks
4. Gotenks
5. Piccolo
Toriyama drew pictures of the top 5 characters to go along with these poll results (which is how we know about them; they're mentioned in Daizenshuu 1's index), and for the 1995 poll he drew future Trunks rather than kid Trunks, so it seems that even well into the Boo era future Trunks' popularity remained constant. Meanwhile, Gohan fell right off the charts...
