Thanks for your answers.
I am still wondering which one to buy...
At first glance, the acurite is attractive with beautiful display, colors, marketing, etc...
But the Tycon seems a little bit less gadget, a little bit more professionnal, with more sensors (UV and light sensors) and the sensors can be separated, not "all in one". It is just my feeling.
I read conflic arguments about acurite and tycon.
Some say tycon is scrap, others say tycon is as good as davis... some say acurite is a lot more modern and quality, others say it is only gadget.
I don't know what to believe.
Finaly I think I can run a PC 24/7 to store the datas from my weather station and post on wunderground. I can use my old Asus "eeePC", dedicated only for that.
The only problem is, if there is a power cut or if the PC restart for any reason, when I am not at home (for example, if I am on a 3 weeks holiday away), I will lose my data (no more data online until I come back from my holidays, and moreover I will lose data for my stats on the PC storage).
As for the live data on wunderground, it seems easier with Tycon. Just connect it on a PC and use the "smartweather" software from Tycon.
Acurite seems more complicated, the software by acurite posts datas to their website "my backyard weather", but can only posts data to wunderground every 15 minutes.
If we want to transfer to wunderground more often, we need to connect a meteobridge on the aculink and then ... I don't know... we need to be very good at technical stuff because there is no software that can read datas on acurite format.
So I think I will buy Tycon but I am still not sure...