I would spend taco tokens. I have never been a fan of stocking up until 300 because it takes you 30 weeks (aka over 6 months to do so). Now I know the argument is that you can pick the vault you want to guarantee those 4* etc but honestly there are only a handful of good rewards anyway that you are waiting 7 MONTHS to get!
Your next best option is to sell of 2* Hawkeye.
The worst option is to sell 1* Venom as you will want that 2500 iso per day, unless you are confident that you can replace your 1* quickly (which may be possible with a lot of standard tokens).
There is always the option to buy HP as well for $.