Have you tried lubing the pistons with brake fluid? Usually frees them up.
If you like the shape of the Avid lever and pivot position then Elixirs would be a good bet. On-one, CRC or Merlin usually have them cheaper than RRP.
Formulas usually have good stopping power and feel but in my experience have poor auto adjust on the pads meaning that the lever throw gets bigger as the pads wear. Not the end of the world and easy to sort but annoying. The older Oro series can be picked up cheaply and have a similar lever shape to avid but are a bit annoying to bleed. The newer RX/R1 pivot further from the bar and can’t comment on the pad wear adjust for these models.
Hope I personally think are overpriced for what they are but they do look pretty if that floats your boat. They are also easy to work on, which in my experience you get lots of practice at……
The best brakes I have used (power, feel and manufacture) are Maguras. 4 sets have been faultless on mine and the other halves bikes. You can pick up Louise brakes fairly cheaply and they perform very well. Fit and forget, easy to work on when the need arises.
Hayes seem to be making a comeback but other than saying that the lever feel is similar to Magura/Shimano I’ve never used them.
Shimano get good reviews but again I’ve never used them.