They all look good but a bit sketchy on the swiss arms one. Never even heard of that name probably another chinese rip off. The first one looks the best imo.
The one on military's first looks like it could be a bit too bulky but its the nicest looking and it looks as if it's the most flexible to when working with it.
Swiss arms make knives and other gear too, im still not too sure with the pull one thing and the whole vest gets taken apart idea i think the MBSS or the M1st one, i prefer the shape and as skilfulmmd said more flexible, whereas the MBSS is said to give loads of comfort to the user, and heck US Navy SEAL use the same styled vest, why can't i?!
Based upon your age (12'ish isn't it?), and probable size, then going for a full assault vest with cumerband is something you will be growing into in about 6 years.
If you are after something that should fit you then have a look at chest rigs as they are a lot more adjustable, and won't wrap round you twice!
http://www.landwarriorairsoft.com/acatalog/Viper_Vests.html like the viper molle chest harness, or another brand, but that style of thing. The SA ciras is the sam style of thing my little brother has (he is 26 however), and it is huge and quite bulky as well as quite heavy.
however if I have remembered your age wrong, then ignore the above
The Swiss arms one looks the same as mine which is a cheap china one!!!
The quility of it however is not to bad at all and for 60 nuggets with all the pouches you can't go wrong in my opinion, after all it is only airsoft not real life.
I just turned 13 actually, and im really sure i want a plate carrier, as Sarni said its just airsoft and the MBSS looks promising as it seems really adjustable!
looks better and better priced, 5.11 make decent tac gear too as i have seen my friends (BatHat's)5.11 Vtac LBE vest thingy, and the 5.11 PC loooks quite small
well the vest captain Price wears in most of the CoD4 missions, my dad has, and when adjusted, fits me perfectly! so..im confused, the ciras might be bogger im not sure, unless i get a lightweight chest rig and get the BHD style body armour?
Well then get it, and then stick it under you bed till it fits. Its your money, but you asked for advice, wether or not you take it is totally upto you.