I know this topic has been brought up time and time again.
But I have a 14.5 inch mid length barrel. If I go with Spikes the st-s1 or st-t2, st-t3?
Or if I go with the bcm there is standard and H through H3.

Can someone break this down for me and help me?
Would really help..
How to choose, why and what to choose?
Thanks!

How to choose, why and what to choose?
Why- proper cycling of the rifle- too heavy-it will short stroke, too light- bolt bounce, so it's like Goldie Locks, you have to find what's best for your rifle's gas system, ammo, carrier and  spring.
What some recommend is buy 2 buffers, H and H2 and you can change weights around to get it just right for optimal cycling of your weapon. Someone who's done this should be along shortly.

I just throw a H2 in everything and it seems to function fine.

Are the 'H' 'h2' are a bcm thing? That's the only place ive seen where you can choose the different weights. I was wanting to get a spikes but didn't know how they all compared to the 'h' because the spikes are 'st-t'

Does the spring have anything at all to do with the buffer assembly?

What is the most popular buffer assembly used in mid lengths?

The most popular buffer used in mid-lengths is the H buffer. There is no "standard" buffer. Buffers are Carbine, H, H2, H3 and Rifle. Buffers marked this way are not just a BCM thing. Spikes is the oddball with their ST markings. Most other companies go by Carbine, H, H2, H3, Rifle. If you're assembling a mid-length a good place to start is an H buffer with carbine action spring. I have 6 BCM mid-lengths with that arrangement and have never needed anything more, one BCM has over 10,000 rounds fired through it and the only malfunctions were mag related.

So I should buy the H kit by bcm or if you think there are better ones out there link me. So buy that then on top of that buy the carbine action spring? Why the carbine spring. And where can I buy that separately ? Is this what you're talking about when you say carbine spring is there a good site where I can buy a H buffer weight and choose a carbine spring so I'm not shopping from bcm then getting a spring from these guys?

Do you have the carbine receiver extension assembly(some call a buffer tube) already? If you are going with a carbine extension (tele stock) then you need a carbine spring, rifle stock=rifle spring.  you can buy the whole thing from BCM or other reputable dealer like Rainier, PK firearms, Primary Arms, ect. see link below. If ^He^ has 6 mid lengths that run well on a H buffer then start with that. If you like the top of the line stuff, the chrome molly springs are the way to go, get the white spring from Sprinco.  

http://www.bravocompanyusa.com/Stock-Hardware-Mounting-Kit-Mil-Spec-p/stock%20hardware%20kit.htm

I wouldn't bother with that spring you posted in the link when you can buy a carbine action spring that is made to the mil-spec from BCM for $4.50.  On their site you have to click the tab which reads, stocks, grips and handguards.. All of the parts are there, buffer, receiver extension, spring, end plate, castle nut or the whole kit. You ask why the carbine spring ? There is only two types of springs, the rifle spring for rifles and the carbine spring for carbines. If you have a carbine then you want the carbine action spring. I wouldn't buy the heavier springs from Sprinco, they make great springs but see how your carbine runs first before going with a heavier buffer and spring. I would buy all the parts you need from one place that way you save on shipping. I don't work for BCM nor do I have any financial holdings in their company. I'm just a customer who knows their products and customer service is first rate. Like I said I own 6 of their mid-lengths and run them hard, I don't shoot off a bench. BTW, I also own a couple of Colts.

Awesome ill get it all from bcm.
So get the H kit then buy  this right here
But I'm still kinda confused.
There are carbine, mid lengths and rifle gas systems. Correct? Mid length is in the middle of carbine and rifle. Is that why I'm choosing to go with a carbine spring?

What you are about to buy is crap. You get what you pay for, buy a vltor a5, you'll thank me.

http://m.youtube.com/results?q=vltor%20a5&oq=vltor%20a5&gs_l=youtube-reduced.3...479.4622.0.5146.7.7.0.0.0.0.0.0..0.0...0.0...1ac.1.5.youtube-reduced.

I have a spike's 14.5 on a mid length.  Have it on a milspec (at least diameter wise) MOE stock / tube kit I got a while back.
Upper is a Billet from TNW.  Carrier is a new DSA.

With an H buffer it runs on real-deal US military type Ammo (Federal, S&B, Winchester, etc.) both 55 and 62gr.

If I run any "tula" it doesn't reliably eject and short strokes often.   If I switch to a 3 oz buffer, it works fine with Tula.  I currently have a low round count in it, so until it breaks in I'll use the lighter buffer.  You may find this type of issue or not, I think its all on the fitting of the parts and what not.

I have another gun with a 16" DSA mid length upper that runs everything thrown into it (go figure) with an H buffer.

No. Gas systems are completely separate from receiver extensions. You can mix and match them.(i.e. rifle receiver extension with a mid-length gas system). BUT, like was said earlier, carbine receiver extension(shorter tube) = carbine spring(shorter spring). and same with the rifle(rifle extension and spring is longer). people typically use carbine stock with a carbine gas system and rifle extension with rifle gas system, make sense?

If you were referring to my suggestion, I just want to point out that the "WHITE Spring" from Sprinco is a Standard Power Buffer Spring. Equivalent spring load to a “fresh” Mil-Spec M4 Carbine Spring. If I was shopping for the "best" parts for my AR I would buy a chrome moly spring. The BCM one will be fine, but some people like having "upgraded" parts.