I can't speak specifically about Plakias but I think the following general description will probably apply.
The only completely uncapped service is landline based broadband, assuming you can get a landline in your area capable of supporting it. Many rural areas cannot, because the cables are long and in very bad condition, although fibre is gradually improving the situation in some areas. I don't think there is any fibre-to-the-home available but they are installing fibre-to-the-cabinet in many villages. That means that instead of having a landline that stretches several km to the nearest exchange it will only stretch a km or so to the nearest cabinet thus improving the speed. Rather like BT in the UK, COSMOTE own all the cables so personally I prefer to buy direct from them. If you buy from any other supplier they are reliant on COSMOTE for the infrastructure so you are buying indirectly from them anyway. I think CYTA have installed their own infrastructure in some areas but I think in Crete they piggyback on COSMOTE.
If you can't get landline based broadband then you are probably stuck with mobile. Other than introductory offers, I don't think there is a big difference in price so you are probably better off choosing whoever has the strongest signal strength where you are. The main mobile providers are using their own infrastructure but there may be some second sellers. I am not sure as I get good landline service. COSMOTE have a hybrid modem that uses landline if it can but boosts speed with a mobile SIM if it needs to. All mobile broadband is capped including the mobile part of the hybrid service.
Satellite broadband, e.g. Tooway, to me is a final option if all else fails, e.g. remote areas with no decent landline or mobile signal. It is more expensive and capped, although overnight uncapped downloading is catered for.
Check out COSMOTE
. There used to be Forthnet but I think they now seem to be marketing themselves to corporate clients. I could be wrong.