If you are in France ? and if this is to do with the auto entrepreneur system then you should choose selling advertising space ( but whatever you do dont mention websites ..on the form.. at least )..
The code will be decided by the INSEE ..and will likely be 7311Z ..
If you want to be certain that you get the code which suits you the best ( in relation to the allowable annual turnover ie € 80.000.oo as selling adspace ..as opposed to just €32.000.oo which applies to those creating websites ) ..then dont fill in the forms on line ..go to the nearest "Chambre de Commerce" to you and ask for the person who is responsible for the "centre de formalities" and fill in the declaration along with them ..and they will send it off to the INSEE for you ( this will stop the INSEE trying to guess what category to put you in ..and maybe putting you into the €32.000.oo one ) ..running websites and related will definitely put you in the 32k "box" as the INSEE always sees websites as "building them for others" which is classed as a service industry and not as a commercial activity ..
The Chambre de Commerce folks know better ;) ..and it's their decision that trumps :) ..How do I know these things ?..I have a friend who is the head of our local Chambre de Commerce ..:)
BTW the tax and "contributions are the same percentage of turnover which ever "regime" you choose ..ie 13% contributions and 1% forfait tax of whatever your annual gross turnover is ..remember you only pay a percentage of what you really make ..if you only make €10.000.oo you'll only pay €1400.oo , only make €100.oo you'll only pay €14.oo ..it's not like micro enterprise ( which is to be avoided like the plague ) where you pay a minimum of around €1800.oo to €2200.oo no matter if you actually only had a turnover of €3.000.oo
I have another friend ( french ) who has just registered ..so have read all the paperwork about the system ..and discovered for him ( he doesnt have internet access ) many french language fora where people were bemoaning the "box" that theye had been put in by the INSEE because they filled in on line and mentioned "website" ..and got put in the box and turnover maximum of website builders for other people ..the INSEE doesnt like reversing it's decisions ..get it right first time ..or you can be into months of "recorded delivery letters"..and long phone calls ..
The french administration is a wonderous thing to behold when it's trying to reverse an error ..but you can do without the ringside seat :)