I just started mining 2 weeks ago. I now have 3 antminer s4's and I recently purchased an SP20 which will bring me up to 7.7TH's.
https://en.bitcoin.it/wiki/Mining_Hardware_ComparisonAlthough it's not the most up to date it shows a quick overview of most of the miners available. But as you read on this forum the majority consensus is the
Bitmain Antminer S4 and the
Spondoolies Tech Jackson SP20I tend to look at GHs/Watt. Pay attention to how many watts the device uses per PSU because you'll still need proper electrical wiring and circuit breakers to support these ASIC beasts. For example if you only have a 15amp breaker you'll only be running 1 S4 or SP20 because they easily pull 1300-1400W on a breaker rated for 1650W(110V). As you begin to expand you'll start to realize you'll have to upgrade your electrical wiring to accomodate ASICs in a residential environment.
Both the S4 and SP20 come in at around 0.7W/GH/s
Antminer S4 ($1200 + $160 shipping) = 2000GH/s/$1360 = 1.47GH/s/$
Spondoolies SP20 ($695 + $119 shipping + $150 1300W PSU) = 1700TH/s/$964 = 1.76GH/s/$
(cyber monday price still available for SP20...$695)
If you can talk someone into giving you a $400 Antminer S4 coupon(Expires 12/15) then the pricing shifts back in favor of the S4 like so...
Antminer S4 ($1200 - $400 + $160 shipping) = 2000GH/s/$960 = 2.08GH/s/$
As far as usability the ASICs are very easy to setup. The S4 requires you to only have to plug in the power cable (14AWG gauge recommended and not included) and a network cable and then remote into the unit from your home network, setup your pool settings and your off and running in minutes.
I've not used the SP20 yet, but I assume its similar, except that I will have to plug an external PSU to the SP20 to give it power. I bought a Rosewill Lightning-1300 1300W 80 PLUS Gold PSU from Newegg for $182 to power the SP20. (P.S. you can pay with bitcoin on Newegg now!)
Look for more information on both of these miners on this forum as there are really good blog posts on each to help get started and configure.