I have aftermarket triggers and I have done these two modes.
For the money and if you have some basic skills the home brew trigger jobs are great.
Actually if you have some advanced skills you can stone and polish the sear and re-harden and have a very slick trigger.
http://www.junkyardgenius.com/firearms/ar-15/ar08.html
http://www.sargenthome.com/15_Minute_AR_Trigger_Job.htm
Disclaimer: If you are not mechanically inclined or have no practical experience I do not suggest you attempt any type of gun repair or trigger work.