They were very different players. Stoichkov mainly a goalscoring wide-forward in the Netherlands 4-3-3 tradition that would still fit comfortably into current tactical trends, while Hagi was more of a genius on the ball, but also harder to fit into a team and get the best out of. You have to account for his inconsistent defensive work and inclination to wander about positionally looking to ensure most of the play goes through him. His style of between the lines, free-role attacking midfielder is quite out of fashion.
Hagi had a much tougher time transitioning to western football from the more brutal Romanian regime. He had a very bad first season at Real Madrid and though he settled in a footballing sense during the second, playing very well and Real only losing out on the league by a point, he opted to move to Brescia (maybe the weakest team in Serie A) in large part because of the Romanian presence there. Managed by Mircea Lucescu and with a few of his international teammates like Raducioiu there. His club career probably would have been much closer to Stoichkov's if he had stayed in Madrid, as he could have filled the attacking midfield position there for the rest of the 90s.
Stoichkov adapted better and found his niche quickly at Barca, but did struggle when he tried Serie A with Parma and failed to fit in again when returning to Barca, before going quickly downhill after that at around 30.