I'm currently using Fulltext but when searching small words like DS-1 or DD-3, I only get results from 2007. I've got about 427685 posts and 52922 topics so the forum is huge.
What would be the best search index to use and how can I make it search small words better?
Thanks!
The "custom" search index is generally better than the Fulltext one. However, you will have to drop the fulltext index before creating a custom one (this can be done from the search method area in Admin -> Search).
How many results are being returned for the smaller words? There is a setting in SMF to limit how many search results are displayed.