Basically the soldering iron market stratifies itself into a few different levels:
Budget Tier:
I'm not calling this **** even though there are some **** offerings because most of the companies in this tier make stuff that WILL work for the average <10 times a year hobbyist . Most of the entires are based around Hakko 936 clones, with a few things added or removed. You can tell because they all use knock-off 936 irons a tips. Companies like: Atten, Aoyue, ZhondDi, etc. You will often seen known companies rebadge products from these companies. My first iron was a Hakko 936 clone and to be honest it served me well without fail for almost 8 years. I used it around 20-30 times a year.
Entry/Prosumer Level:
These are much higher quality. The fit between the heaters and tips are tighter, the quality of materials is nicer, they hold their temperature much better, have higher wattages, longer lasting tips, etc. You are very likely to see them on a pro's work bench but also might see them on an assembly line. Companies such as Hakko, Weller, Ersa and older Pace stuff are prime examples. The entry level stuff from each of these companies typically hits right around USD$100 and will last decades.
High End/Industrial:
These are the dogs nuts of soldering irons. They are meant to be abused, used 24/7 and make soldering as quick and easy as possible. Typically RF Induction based, most of these will make quick work of even the MOST difficult soldering jobs. Companies such as OKI/Metal, some Ersa, Pace and JBC (the best of the best at this time) are typically who you will find at this level. Expect them to be PRICEY (easily $500-2000) but if you need one then you know it. They often offer VERY thin light handles for easy precision soldering, LONG lasting tips, features to extend tip life, the ability to solder even the most difficult materials (such as to large copper ground planes), etc.
A bit of info about types of soldering irons:
Cold-heat resistive:
**** for electronics work, can easily kill static sensitive components
Butane:
These are decent for cordless soldering, temp control is borderline non-existant so its easy to lift pads and traces on a PCB. Much better used for splicing wires.
Ceramic Heater:
This is the most common type of soldering iron. It uses a ceramic heating element to heat a metal tip. Most budget and prosumer level irons use this technology. Temperature controlled irons include a themocouple in the ceramic heter or tip to control the temperature via a PID loop. The most common variant of this is based around the Hakko 936. It incorporates all of the needed features in a very nice reliable and inexpensive package. For this reason, it has been copied and reworked continuously in the aftermarket.
RF Induction:
This is the new kid on the block in terms of soldering. Its pricey but offers some very solid benefits for power users. RF induction works on the same principle as a induction furnace. A piece of metal is placed within a RF coil and the high frequency AC causes a rapid heating of the metal. In this case, the metal within the coil is the tip of the soldering iron. This allow for a rapid heating of the tip with heat times typically around 3-10sec from cold to full temp.
There are two different types of RF Induction in use right now. Fixed temp and temp controlled. Fixed temp was popularized by Metcal (now part of OKI) it exploits the Curie Point of the metal to control the temperature. The upside to this method is that for assembly work is you pick the right tip for the temp needed and its physically impossible for the worker to mess it up. Very useful in GMP environments. The downside is if you need a different temperature you have to purchase a different tip.
On the other hand, for temperature controlled ones. The thermocouple is integrated into the tip as with ceramic heater irons, and the RF is dumped into the iron until it reaches the proper temp. Most modern irons, like from JBC, can go from cold to set temp in under 3 seconds. This rapid heating now allows manufacturers to turn off the iron when it sits in the cradle rapidly prolonging tip life. This rapid heating also means that they can use low thermal mass tips (which cool down quicker) and higher wattages to compensate. Its not uncommon to see an iron running at 150W or more for short periods of time to allow soldering to large ground planes etc. Because they cool down quickly and shut down in the handle, the 150W is not a problem for tip life.
