Hi.
You will get tons of replies to this.
Everyone has their own preference as a starter.
What is your budget?
Do you have a first project in mind?
Older Forumites may suggest an 08M but, and just my opinion, I would start with something a little bigger and better so that you can use most/all of the available commands.
However, if your level of electronics experience is limited I wouldn't suggesting going for the biggest just in case you pop it due to mishandling.
You would probably want to programme in BASIC.
Have a look at Manual 2 and study the commands.
You can get this on-line PICAXE Manual dropdown.
To get a summary of the PICAXE variants look in Manual 1.
This will show the pinouts, the simple circuits for downloading code from PC to PICAXE, and some examples on how to connect to the Real World.
May I strongly suggest one thing.
Many, many people have trouble at first with the download circuit.
I suggest getting the cheapest project board for the PICAXE you choose.
The PCB will have a download circuit on it.
It could save hours compared to using breadboard.
If your PC only has a USB connection then you will need a USB-Serial adaptor.
May I suggest a second thing.
I have seen numerous and prolonged threads because people have been 'economising' and buying a.n.other brand of adaptor.
Buy the AXE027 and install the drivers available from Rev-Ed.
The extra quid you spend on it could save hours of posting and grief. Cheaper than Just For Men.
If you are feeling flush then consider the AXE091 Development Board.
You will be able to do quite a lot of prototyping with that.
Not cheap but could save hours of faffing around.
Enjoy.
Oh, get yourself at least 2 spare PICAXEs... just in case.
And a bag of resistors too - e.g. 4K7, 10K, 1k0, 470R
And a few capacitors as well. Whilst the manual doesn't seem to mention it, it is good idea to have a 100nF (or so) ceramic on the PICAXE power pins.