There really isn't a simple answer to this question of "best receiver". It's not like buying, say, an electric kettle, where they all have the same function. Different receivers satisfy different requirements.
For example, the Nokia Mediamasters are not comparable to the other two you mention. The Nokias are digital only. The other two include analogue. The Nokia has no built-in positioner. The other two do. So do you need analogue and positioner? If you do, then however good the Nokia is it is useless to consider it.
With regard to hacking into CAM systems... ...CAMs are the modules that are inserted into the receiver. They are designed to decrypt different kinds of encrypted signals. These include Irdeto, Nagravision, Seca/Mediaguard, Conax, etc. If you want to know which of those is the most easily hacked, the answer is Irdeto & Seca. But again it is a strange question. Each provider chooses a particular encryption signal. The question you need to answer first is: which channels (of which providers) do I want to receive? There's little point in buying an Irdeto CAM for example - however easily hacked - if you want to watch, say, the Taquila package - which is Seca/Mediaguard.
If you decide to go for a Nokia and want to load the Overflow software, you should first check out the specifications. There are too many functions to list here. Perhaps you should start at the Dominance web site: http://www.dominance.net/overflow/ I think the info you want is at the "DVB2000 info" link on that site.