What difficulties do you have with your current rig? Is it possible to fix those?
I think if you ask 10 people you will get 20 different opinions on what is best.
To start with it depends on how important this or that is to you personally.
- how big?
- how expensive?
- do you have familiarity with this or that flight controller or firmware?
- are distance and endurance important?
- are advanced navigation (waypoint and RTB/RTL) important?
- is ease of transport important (backpack, etc.)?
- do you want to fly behind trees at all (RF frequency)?
Some things interact, for instance to fly behind trees a bit better you want a lower RF frequency, but that needs a bigger antenna which requires a larger aircraft.
The one thing I would suggest is that you have plenty of motor power (for a quad) and plenty of battery capacity.
I've bought several pre built FPV rigs in the 70mm to 150mm size range and they are the easiest to transport and use. I have a 500mm FPV rig that has a second camera on a gimbal and can do waypoint and RTB. I have a couple fixed wing FPV rigs. If you want distance or endurance you must go fixed wing.
From me you will get that good quality RTF rigs are the easiest to setup and fly, but I prefer to build it from scratch with inexpensive components. I like small quads for flying close (<100m). I like my 500 quad for 100m to 500m. I like my fixed wing for endurance and long distance. I also have used at times 910mhz, 1280mhz, 2.4ghz (with 72mhz RC), and 5.8ghz video rigs.