online class metatrader 4

The editors are roughly similar, the MQL5 one has a built in debugger and some tools that make programming a tad bit fast like block commenting, function search (or drop down menu) and updated assist menu that actually looks at your variables and functions. That makes the version 5 more "powerful, friendly and easy to use or learn".

If you're asking about the language itself though I find that the developers complicated things a bit and personally I found MQL5 more difficult to learn. Where in MQL4 you did 1 line to do a thing (most notably getting ask/bid price for example or the whole timeseries functions) you have to write at least 1 to 2 more lines for the same stuff in MQL5. Not more difficult, but more stuff to learn and to me a bit more annoying. However the introduction of objects and events in MQL5 made it possible to code complex ideas faster and enjoy a more readable code.

If you're just starting out, go with MQL5. It's probable that by the time you learn it and manage to code an EA you want to put to use on real acounts, we'll all be using it. Till then the metaquotes demo accounts are open to anyone.