You can pretty much classify intercoolers into 3 classes. The original JDM ones, the china/ebay copies and the USA made ones.
The major JDM options were:
1. Greddy/Trust - this was the most popular sidemount for the sw20.
If you can a good condition second hand one, that would be my pick for sidemounts.2. Apex'i - not as common as the greddy. was a thicker core than the greddy.
3. HKS - much rarer than the greddy, it was similiar in performance, but you'd be hard pressed to find one of these nowadays
4. ARC - Very expensive, but didn't perform any better than the greddy. Virtually impossible to find these now.
5. Phoenix Power - Essentially a modified Apexi core, with a bolt on pipe so that you could never "blow an intercooler hose". Also fairly hard to find these days.
China brand:
XS power, Monsta etc are just alibaba products rebadged and they were all a greddy copy essentially, so go this if you don't really care about brands and just want a cheap intercooler option that works. Fitment won't be quite as good as the original greddy, but silicone joins are pretty flexible so fit doesn't have to be 100% for it to work.
USA Made:
Berk Tech used to make a sidemount, claimed to work better than anything mentioned above, but i never got to see one in action. Due to price, they were never really that popular. They stopped making this a while ago so again you'd have to find one on the second hand market.