im looking at theses amps currently and i want to upgrade, currently i have a little samick thats old and its kinda bad



or a marshall G80RCD

im open to suggestions i have also thought of a line 6 pod but im not sure, i like to play greenday, ac/dc etc i might also be getting a strat affinity and might try stratty kind of music, im still kind of a beginner
In that price range go used. You won't get anything good for that price new.

I would recommend a Peavey Vypyr. They run pretty cheap used and are very good amps for practice.

Also, you should have posted this on the Guitar Gear section
Go for the Roland Micro Cube Gx ... only 2 watts but damn its so loud... it sound really good... its a "smart" amp :P .. you can easily jam with a drummer (thats to show you the volume) It has all the effects and a memory (to save your settings)
Biggest Vypyr you can afford. Or maybe the Vox VT series for lower gain models. Also based on the two bands you listed I'd be looking at a different guitar, the Affinity's are hit and miss and not really suited to that kinda music - I'd suggest something like an Epiphone G-400.

Used gear is your friend, so long as you check it out first.
Agree with the Vypyr, but that's because I don't have experience with the Roland, so I can't comment.
And the affinity will be fine. As long as it has a humbucker, it will play greenday, ac/dc, pretty much anything just fine. Worry more about how the guitar feels and plays than whether it suits your particular style of music.
Harmony: Stratocaster
Alvarez: F-200
Schecter: Omen 6
Fender: BXR-60
Dean: Metalman Z Bass (Betty)
Egnator: Tweaker 15
Pearl: Maximum
Custom: Harley Quinn Bass
Custom: TK-421 Explorer
A steadily growing supply of pedals