DDLJ (1995) is more popular than HAHK (1994) because DDLJ is an epic love story whereas HAHK is a typical family melodrama.
The stories of both these hit films are totally different. The actors are totally different. Both these films have their own achievements and it is not fair to compare both of them.
However personally I admire DDLJ more than HAHK being a die-hard fan of Shahrukh Khan. The popularity of HAHK died after a few years but DDLJ can be watched even now.