If you are buying new, my stupid answer is to get one of those modern instruments which have reflected, incident, flash and spot metering all in one device.
Reasons to do it:
- you get more light metering for your bucks;
- in the future those device might become more expensive than they are now;
- you can explore different techniques without having to buy a new device (which might actually prevent experimentation);
- you travel lighter than if you have to carry incident and spot (one day you will consider it if you use slides).

If you buy second-hand, any modern silicon blue cell (SBC) light meter will do great, especially if you don't choose out of the usual suspects (Minolta/Kenko, Gossen, Sekonic). Your most important choice will be between analogue reading and digital reading.