I would say the defining thought is what YOU want. If you always wanted a sw
tank and you've got the means and patience for it then you should do it. But if you just want to start fishkeeping then maybe the FW
tank is your best bet. Freshwater isnt quite as expensive and can be challenging too depending on what you keep. Also, if you get a large enough tank it can easily be converted over. You'll just need a few different things to buy. You can even run a sump on FW
tanks too so you could start off with that in FW
. You can also use a canister filter for saltwater too, I have and with great success.
It really comes down to what you personally want. Either way this forum is a great way to make fish buddies and the information is plentiful on either side.
How big of a tank were you looking at buying? That can determine alot too. If you only have room for a 55g say, then you might wanna start with FW
. I think a 55g is a good starting point on sw
tanks in my opinion as every drop of water you have makes the system more stable.