The most flexible receivers are the new generation of linux receivers. These are high end enthusiasts reeceivers and not easy to learn.
For something you can get out of the box and have up and running in half an hour then a FortecStar or Technomate is a good investment. Echostars ahve their fans as well, but can be a bit quirky for some users.
For my money the best receiver is the Technomate TM-1500ci+ super, read review by the wizzz in section cunning called "Receiver Reviews", as for the card you don't say what you hope to watch ie, films, football, mature content !
The Dreambox 7020: because you can put a huge hard drive in it and it's got a huge following and therefor great support. It uses linux so will be supported/developed for, for a few years at least. CF slot built in, 2 Card slots, and 1 Common Interface slot. Can record onto it's own hd (if you add one) or a computer on your network. You can even plug an ADSL and/or Cable modem into it and connect to the internet without using a pc at all. Emulates almost every card on the market, with no further purchases necessary.
Have you bought one yet?
I say without doubt that on paper at least, the 7020 is the best receiver. disclaimer: ..for me :-googly
It's a bit like asking is a Ford alright, is a Fiat alright, is a BMW alright. Which model are you after as each maker has many different models ?
I have had a Humax before and I thought it was an average receiver, no where as good as my Technomate but other people might disagree and think that the Humax is better, especially if picture quality was of uppermost importance as the Humax does give excellent picture quality.
If you are looking for a receiver which will work with all CAMs and cards on all encryptions, then it doesn't exist, you cannot future proof to that extent.
The fact that the Dreambox runs on Linux is a bit of a red herring, you need to know nothing whatsoever about Linux (I don't and have successfully run mine for a long time now). You merely need to know how to use an FTP program and possibly Telnet from your PC to the Dreambox. I would however still not recommend one to a beginner who is not prepared to do a lot of reading (and understanding) first and the same would go for receivers which require regular flashing by RS232.