Hallo Hatem,

I'm a little bit confused. Why are you wanting to build a 'simple' fuction generator with the help of microcontroller? Normally, starting point of development is list of specifications product must fullfill.
So, before anyone can give really reliable recommendation, we also need to know these specifications. What's the range of frequeny of interest? What about the precision, in terms of harmonic distortion, frequency constancy, amplitude constancy, jitter, temperature suscceptibility? What has to be adjusted? How fine frequency shall be controlled? 10Hz steps, 1Hz steps, 0.1Hz steps? Should there be any software controlling, something like remote control via PC? E.g. that PC measures frequency behaviour of some DUT at some very certain frequencies, without the need of human operator to adjust the knobs?
If there is no need for remote control I would take good old XR2206, ICL8038 or modern MAX038. If you need high precision of frequency adjust use an additional PLL-loop (e.g. consisting of 4046) and control frequency of (e.g.) XR2206 by the help of VN82, or similar. If you need controlling amplitude you can use (e.g.) LM13700.
So, even when you need remote control of frequency and amplitude analog signal generation can be advantegous. Microcontroller could be used for instance to have communication with PC, programming PLL loop, programming VCA (voltage controlled attentuator) or monitoring amplitude of signal.
There are thousands of ways to develop function generator. So, please give us an idea of specifications it should fullfill.

Bye,
Kai