Just for the sake of clarity:
CRP = Pooley's version; ARC = AFE version; E6-B = ASA version; TPS = Transair version
CRP-1 ; ARC-1; E6-B; "Jeppesen Slide Graphic Computer"; TPS-1
Designed for Private pilots - the CRP-1 is the standard everything else is compared to. CRP-1 & ARC-1 are essentially the same with all the features of the others; E6-B and the Jeppesen one are (I believe) missing some metric / imperial conversions which can be useful as they are designed for the US market. E6-B comes in multiple materials and sizes (which all do the same thing).
CRP-1W ; TPS-1 with wind arm
As above but with wind arm which some people prefer. It saves needing to use a pencil to work out winds
CRP-4
A budget CRP-1, made of card instead of plastic and missing the rotating cursor on the computer side.
CRP-5; ARC-2; TPS-2
The upgraded version of the CRP-1 / ARC-1 for "Professional" pilots. If you plan on going commercial, get one of these. They are larger, so can be more accurate, and they deal with the higher speeds required for commercial aviation. CRP-5 is the standard (certainly in UK). ARC-2 also includes the ability to do a couple more calculations but the ATPL exam questions are based on CRP-5 - and the answers you get with ARC-1 will be just slightly wrong...
CRP-5W
As CRP-5 but with wind arm. For the accuracy required at pro level, the wind arm is reputed to be not accurate enough so just gets in the way
CRP-8
This is designed for Microlight users and so deals more accurately with low speeds
There are other pooley flight computers but they aren't commonly used (such as CRP-6 or CRP-9)
Hope this helps!