Buy the one you think looks cooler than the other because that's about the only difference. There are no bad guns. Just the ones you don't like.
For a scope - Airsoft has limited range. I have several red dots and scopes because I think they look cool and can afford them. When it's time to play the scopes come off. If you can't shoot with iron sights in airsoft then you simply can't shoot. It won't make you better but there are some instances when types of masks and such make it hard to use the iron sights so you can make up for it by raising a red dot or something. Get a cheap one or an expensive one. No one can tell you what to buy. Get what you like but airsoft is like golf, you can't buy a good game, just practice.