I'm planing to buy a merlin head and control it with Arduino. Is anyone here having experience with this an can tell me if this is still a recommendable way and which software for Arduino is the best?
There is no Arduino software for this.
Just one question ... why look for an Arduino solution? I mean, there is a first class PC-notebook-based and Nokia-mobile-based solution already - the Papywizard software controller - that has taken more than 5 years to develop into its present form of excellence, and it's FREE. Then there is the T&C touch controller sold by Kolor which is an excellent product costing a couple of hundred Euros.
It will take someone at least 2 years hard work to develop an Arduino solution- the standard Arduino IDE is unsuitable because it does not provide a multi-tasking OS, which you will need to provide accurate timing for driving the stepper motors while at the same time updating the angular position in the display and scanning for user input. It's a complex project and the market for pano photography is quite specialized, with only a few thousand enthusiasts with motorized mounts. It's hard to justify anyone making another controller when the existing ones work very well.
Kolor can supply you the whole lot including the Merlin head, a Bluetooth radio interface and controller - called Panogear.
Alternatively there is the new AllView motorized mount, which comes with its own SynScan hand controller for pano shooting.