Whatever it originally came with. Usually a 16, cept for my 38 special 1911 which is I believe 12. I figure the manf has a better idea of what works correctly then I do and it is just as bad having a overly strong spring as it is a weak one. I can only see a lighter or heavier one if one shoots a +P or downloaded round all the time.  

The only thing I have used other than 16# is an 18.5#. The 16# springs work well in my guns and I have no reason to change the specs. I am not at all concerned about wearing out a 1911 or excessive battering, or any other such nonsense. They are tools that were made to be used. If I wear them out, I'll replace them. However, somehow I am sure that better men than I have tried, and been unsuccessful in wearing out a 1911.

[email protected]

I run 18.5# Wolff recoil springs in all my 5" 1911s, never had a problem.

Up until recently I have always used a 16# recoil spring.
I purchased a Para  P14-45 last october,installed a 16# recoil spring in the pistol to replace the original spring,and noticed it was performing differently than it had been.Function was 100% but the cases were ejecting out to 6'-8' with some cases going further,primers are wiped,guide rod head started showing light peening and was getting sharp spike to the hand.All signs of a weak recoil spring that Ive seen before.So I reinstalled the original recoil spring that came in the pistol.
First thing I noticed was the original recoil spring felt stronger racking the slide.So I got out another new 16# spring...samething the original spring was stronger.
So I compared the original factory spring with the 16 pound springs.The 16# springs checked at 32 1/2 coils and wire diameter is .044".The original spring was 30 1/2 coils and is .0455".
Installed the old original spring back in the gun and test fired it.The pistol had calmed back down,cases ejected out to 4' in a nice little pile at 3 o'clock.No primer wipe or spike to the palm.
So I contacted Para to see what spring they use from the factory.The pistolsmith at Para said they use a 18# conventional recoil spring and highly recommend that it be used.And I see why.
The only difference I can see in the Para P14 and the other 1911's is the para uses a radiused firing pin stop,actually its ramped compared to the others.From what Ive read plays a huge role on how fast the slide opens.
In my research of the springs I found that not only Para,but Wilson Combat and Baer both recommend the 18# recoil springs for their pistols.
I also read an old article that mentioned the Marine Corp. had used a 18# spring in the 1911 for reliability and function.
So as mentioned by fxntime,use whatever came in the pistol and is recommended by its manufacturer first of all.The information in the Wolff catalog,I.S.M.I. etc. should be used as a general base line but the manufacturers recommendation should be followed as I have found out.Not all 1911's are built the same.Minor differences in manufacturing and setup can play a role.
That said,I picked up a couple Wilson Combat 18.5# springs from the local gunshop this morning.Which Im told is made by Wolff.
Installed one in the Para P14 and it runs exactly the same as it does with the factory 18# Para spring....perfectly that is.
The ammo I use for practice is UMC,WWB,PMC and Wolf occasionally.Carry ammo is Rem. Golden sabers 185gr.-230gr. and Win. silver tips 185gr..
Fired an assortment  of the ammo to include the carry ammo and Wolf in pistol and the preformance is perfect with the 18.5#.Reinstalled the 16# spring and the pistol is a bit wild,with all the signs of a weak recoil spring I mentioned above.
So its 18-18.5# recoil springs in my Para...nothing else.
I plan to try the 18.5# recoil spring in the Bul and Mil-spec just for kicks and giggles.But from what Ive read alot of folks prefer the 18-18.5# springs in the 1911 these days.

I run a 16.5 lb Wolff variable in my Colt XSE.