i cant say anything about hydro, never heard anything about them. But i can recommend hagen and rena filstar xp1/xp3. Many people are very happy with them and they dont have the steep price of the eheims. It isnt as quiet as an eheim though, so if noise doesnt concern you, id just go with one of those. With cannisters its all about the size of the cannister to hold the media, and about the flow rate. Many people are happy with the jebo units as well, they are kinda eheim proffessional remakes. good luck