Help in selecting Mechanical Watering Timer

[Gerardo]

Hello Tomatoville:

I'm about to purchase a Mechanical Watering Timer. Need some help in choosing one.

http://amzn.com/B006FLGHGE orbit

http://amzn.com/B0015AP1QM nelson

http://amzn.com/B001P80H22 dramm

http://amzn.com/B00IJG4FEE Gilmour

Pops is technologically challenged, so I'm hoping turning a dial can lead to better results.

One will go on my low flow gravity set up. Another will be directly on the house water circuit.

Any guidance appreciated.