I haven't tried the one in Dokki, but generally speaking, Gold Gym is relatively the cleanest gym around. I would recommend joining it because it is a also a very good venue to meet new folks. You also get 500LE discount if you are an HSBC card holder.
On another note, do not be alarmed with several of the customs in the male locker room. You'll notice the following, so act normal and don't be alarmed or show any signs of confusion.
1) Males can and will kiss each other on the cheek while both are naked. They can still be straight guys
2) Males might start praying on the floor near the bathrooms, so if you came out of the bathroom, don't be confused, just walk normal. They might also be praying in front of your locker, so simply wait until they finish. Do not start being pushy because they are praying too long and you want to get your clothes to leave. Be very respectful. Also watch out for rugs on the floor. They are used for praying, so don't step on them and walk around the rugs.
3) Some males might start washing their feet on the sink. You are probably used to seeing only hands on the sink, don't be disgusted nor confused. This is a very popular custom.
4) Some males might wash their socks on the sink and then wear the wet socks. Again, do not be alarmed or show any signs of confusion.
5) The background music and/or TVs might stop during certain hours. This might be because one of the staff members decides he wants to pray in the bathroom and he doesn't want you to listen to music or watch TV. Again, don't go complaining to the management about this issue.
6) Many trainers might start talking to you about religion, try to be very respectful. For example, once a trainer kept talking about religion with a bunch of French guys and then the trainer was obsessed with the religion of the French soccer team. He started going on about the correlation of religion with the skill of the soccer player. So avoid those types of conversations for your own sake.