Someone asked for a basic comparison between the Rocket espresso machine line up. The following is a comparison of the main differences. There are other small differences between them, but this is an good overview comparison of the most important feature differences.
Appartamento - good heat exchange machine. It doesn't have a PID and the boiler isn't insulated (insulation provides temperature consistency that is highly important to making the best flavored espresso). Has a vibratory pump and cannot be direct connected. A heat exchanger is good for someone that does primarily milk based drinks. Heat exchangers have less control over the brew temp and you have to learn how to do the heat exchange flush and do it consistently every time.
Rocket Mozzafiato Type V - Heat exchange machine similar to the appartamento, but has a PID for better temperature adjustment and has an insulated boiler. Also has a metal cup rail vs plastic. Like the Appartamento it has a vibratory pump and cannot be direct connected.
Rocket Giotto Evoluzione R - Heat exchange machine similar to the Mozzafiatto. Has an insulated boiler and PID temperature controller. Has a rotary vane pump (quieter, longer lasting and needed for direct water line connection). Has a water tank or can be directly connected to a water line.
Rocket R58 - Double boiler machine. Can't really go wrong with any type of drink you tend to make, but a double boiler is a good machine to get if you make about half espresso only and about half milk based drinks. If you roast your own beans or change your beans often, the increased temperature adjustment control due to each boiler having a dedicated use will improve drink quality and be easier and quicker to dial in shots. One draw back of a double boiler like the R58 is when they run on 15 amp, the power is pulsed back and forth rapidly between the two boilers to heat each one. Most of the time this won't be noticeable, but if you are making several drinks in a row, you will sometimes run into recovery time... Meaning you won't be able to use the machine until the steam and brew boiler temperature get back up to temperature. With a heat exchange machine you will run into this less often because it's just one boiler that has to be heated.
Rocket R60 - Another double boiler machine like the Rocket R58. The biggest difference between this machine and the R58 is that the R60 has pressure profiling. If you are someone that has a very delicate pallet, you would appreciate the tweaking you can do with adjusting the pressure profiles. A good machine to compare this one to is the Vesuvius pressure profile machine.