4 PRO is a good head. Warm sounding, lots of bass, clean and plenty loud when SET CORRECTLY. My problem with the head was the lack of string clarity. If you want edgy pick playing tones, they were quite hard to get out of the 4 PRO. I constantly had to reduce low end content out of the head just to get a usable tone in many situations.
EBS is a whole different ball game. I will not comment further since my time of using the heads is quite limited.
Purchase whatever you want, but make sure to take advantage of 30 day return policies, meeting with bass players and playing their rigs, and check out youtube videos with the gear you like. When listening to the videos, keep in mind ALL GEAR hooked up with the amp heads. Different cabs, rooms, effect pedals and players will give you different versions of the amp's abilities. Use headphones or a speaker system with a subwoofer too. PC speakers are NOT a good choice for evaluating bass gear.
Buying used is a GREAT idea.
Korean-made SVT 4 PRO's versus American-made 4 PRO's - I owned one of each: not a difference in sound. Parts were most likely different, but I had the same result with each head.
Are there other brands you want to look at? Why are you only looking at these two brands?