Well that all depends…
- Are you creating a project for someone who’s paying you that you need to be sure it works. – Use stable.
- Are you simply experimenting and tinkering with code and not afraid to make small/big changes later and know Bootstrap already? Use alpha.
- If your completely new to Bootstrap and never touched it before. Use stable.
Alpha may have changes later on. So it would be pointless learning something that isn’t set in stone and maybe completely different later.
And the other thing is can I use both 3 and 4 on a same site or there
will be issues?
There will be lots of issues. Besides maintenance headaches, it would defeat the purpose since they would both attempt to overwrite each other, and top it off, your page load times will go up since your attempting to load 2 frameworks. (The less code the better!)
I would also recommend starting to learn software terminology to make better sense of things when you start comparing libraries/frameworks.
i.e.
-
Alpha = Very uncompleted, will introduce features, or big changes. (Good chance of bugs that have or haven’t been noticed yet.)
-
Beta = Very close to completion, will not introduce features
(usually not anyway).
Hope this helps, and good luck!