The Sbach 342 is beautiful with its sleek lines, faster roll rate, but is more demanding being unstable and very light in pitch, whicvh may catch the unwary.
The extra300L is more suited for the job, can be found used for a reasonable price around 180-220 k euros,
Is fully certified with a very good back up in terms of spares and service. If you break anything the costs of spares is astronomical.
Both aircraft need qualified pilots and instructors, and would not be ideal for ab initio basic aerobatics, or tailwheel training, they are expensive to run, virtually undestructible in the air but delicate on the ground and in the take off, landing phases.
The extra300l has very limited fuel capacity in its main aerobatic tank, suited for short sorties, and bear in mind that 200hrs flying a year would mean 5-600 flights. And hourly rental costs average 600/800 euros per hour, these aircraft are not intended for solo rental, in this case be very very selective to whom you would let fly solo.
In the end it s a matter of how much budget you have for the task, if you intend to generate income with flying them, either you have good cash, a good booking agenda for airshows or a good potential in terms of paying customers. Do cosider if you are an ATO to offer Uprt-Loc training which will be mandatory soon as a source of further income.
They are fun, will markedly improve any one skills, if you have the financial side secured go for it, you will not regret it. I'd go for the Extra, if you are wealthy and want an expensive toy for yourselves get the xa342 if you can find one, possibly certified, snd be prepared to spend 50k euros more tant the 300L