Arduino Newbee: Help in deciding which arduino to buy

Hello Arduino community :)

I need to digitize input voltage into a graphical (time vs. voltage) display.

The input voltage comes from the Luxtron 712, a really old fluoroptic thermometer that converts temperature into a voltage reading.

The Luxtron 712 has a + or - 5 Volt capacity. The Luxtron also has 2 different temperature probe readings at any given time.

I wanted to use LABVIEW to digitize and graph temperature converted into voltage but its expensive so, I am looking for alternatives.

Any suggestions as to which Arduino model would suffice my needs?

Attached is a pic, the green box is what I'm working with. Any ideas? I am also open to something else besides arduino but arduino seems very promising.

If that is all you want to do, a Uno is an obvious choice. It is cheap, convenient, and well-supported.
Some useful alternatives for graphic display are:

PLX a macro for Excel. See here http://forum.arduino.cc/index.php?topic=437398.0

Bluetooth Graphics Terminal which is what I use

Blynk

All are free. All have their own features and limitations

I like the Nano because it's breadboard compatible, small, and easy to incorporate into a project.

I'd only recommend an Uno if you want shield compatibility or need the extra current its 5V regulator supplies. The super annoying thing about the Uno, Mega, Leonardo, and any other Arduino board in a similar form factor is they screwed up the spacing on one of the headers so it's off the standard grid, making it not compatible with ordinary stripboard or perfboard. You can buy protoshields with the right header spacing but it's just annoying we're forced to do that because of a screw up years ago that was never fixed but instead excused as a "feature".

If you want to go for the smallest size and lowest price the Pro Mini is the one. You will need a separate USB-serial adapter board, which makes it cost the same as the Nano but the adapter can be used with multiple Pro Minis so you can get by with only buying one.