This site has been great fun, but it has run its course, and it is time to move on. Please get what you want from the site before January 1, 2020. Some pages will move to another site but most will go away.
The Raspberry Pi is a microcomputer board with an ARM core in a System On a Chip (SoC) with RAM piggybacked on top of it in 256MB to 1GB configurations, and having some form of network connectivity (with the exception of the RPi Zero and RPi 1 A+). It is expected on those units that you will add a network dongle if you need to get to a network.
There are several versions of the Raspberry Pi board that are available at the time of this writing. I believe the following is a complete list. Several versions may fall off in January 2020, due to obsolescence.
|Model||# Bits||# Cores||CPU speed||RAM||ETH||Wireless||Bluetooth||Form Factor|
|Raspberry Pi 3 Model B+||64||4||1.4GHz||1024MB||1GB||2.4GHz/5GHz||4.2/BLE||Standard|
|Raspberry Pi 3 Model A+||64||4||1.4GHz||512MB||-||2.4GHz/5GHz||4.2/BLE||Compact|
|Raspberry Pi 3 Model B||64||4||1.2GHz||1024MB||100Mb||2.4GHz||BLE||Standard|
|Raspberry Pi 2 Model B||32||4||0.9GHz||1024MB||100Mb||-||-||Standard|
|Raspberry Pi 1 Model B+||32||1||0.7GHz||256-512MB||100Mb||-||-||Standard|
|Raspberry Pi 1 Model A+||32||1||0.7GHz||256MB||-||-||-||Compact|
|Raspberry Pi Zero W||32||1||1GHz||512MB||-||2.4GHz||4.1/BLE||Zero|
|Raspberry Pi Zero||32||1||1GHz||512MB||-||-||-||Zero|
The 3A+, 3B, 3B+, Zero and Zero W are the current release versions, although RPF says they plan on continued production of the others until early 2020. I would still stick to the later versions, simply for their enhanced performance. It is not unreasonable to spend $45.00 on a computer and power supply to run a resource intensive application, so the 3B or 3B+ are great for computer-like problem solving. If you are solving a problem that doesn't require a full desktop, the Zero and Zero W might be a better match.