Hey Jeos, welcome to AP.com!
I think most players end up having a great time with whatever they choose.
If you are located in Oregon, a good move would be to check out similar models at local shops like Extreme Velocity, Thunderkiss NW, Airsoft Outlet NW, & Oregon Airsoft Arena before buying anything. This way, you can get your hands on something to see how it feels & get a good deal from someone that actually plays on the same fields.The website you found these items on is actually based in Toronto, Canada. Are you based in Ontario?
At any rate, I am not familiar with ASG but have had good experiences with anything Elite Force. Also, the features of the Beretta seem pretty cool including the easy breakdown for cleaning/upgrading & the folding stock will be useful in the field as well as packing up for travel. It uses the M4 mags which is awesome & has rail space for days while that particular M4 only has a single short rail for the carry handle sight.
According to that Mach 1 Airsoft site, both AEGs have similar performance, so I would pick the one that looks more fun to shoot. I was able to find that same Beretta on Evike for about $100 less:
http://www.evike.com/products/46840/I personally use a KWA M16 & thoroughly enjoy it. Maybe someone can speak to the ASG products.
I hope this is helpful!