help me choose and decide between two ssd drives

[ripo66]

Hello Everyone and good day 
I'm trying to decide between two ssd drives
I Adding an images of this 2

http://imgur.com/a/2zVia

http://imgur.com/a/puuaW


One is "SanDISK SSD PLUS MODEL SDSSDA-240GB SATA 6G/s "

THE OTHER IS " SanDISK X300s SD7SB3Q-256G -1006 "

i have a couple of Questions

1) Which one is better ? And newer ?

2) If I connect them to pc the one with 240GB show only 223GB and the one with 256GB Show me 238GB It's a 15GB Difference in Capacity storage IN THIS CASE

What you recommended ?



3) they both sata III (3) ? if no , its Critical difference between sata 3 and sata 2 ???

4) I plan to used the ssd drive with adapter cable usb Directly to computer like an External Hardisk to backup some files and stuff it a good idea ?

USB adapter connection speed will not fall down?
5) Maybe After a while I'll use it to connect internal hard drive for the operation system so which one better for two cases

I appreciate your help and want to Thanks in advance everyone

 

[PP Mguire]

X300 is better, they're both SATA3, and only use it external if the enclosure is USB3, cable is USB3, and port connecting it to is USB3.