Best extractor fan for bathroom??

[Mobrown]

Hello hope you can help, we are in the process of returning the bathroom, have a four price going but I have no idea what type of fan we need, Measurements of bathroom are 2.7m high,floor space is approx 5m2, all walls are approx 20m
Fan will be ceiling mounted venting through the roof but whats the best fan? Did buy a

 

[Mobrown]

Sorry did buy a manrose fan but took that back as it had quite bad reviews, needs to be efficient and quite, any advice with links would greatly be appreciated.

Thnanks

 

[Mobrown]

Sorry all walls combined are approx 20m

 

[AWheating]

have you asked your electrician what he/she recommends?if its a long duct run i would go for something like a rvk in line fan with insulated ducting. you can get them with and without speed control i believe.