Rebuid and reorg both are good but it depends on fragmentation of index. Microsoft recommends rebuilding if fragmentation is over 40%, reorganizing if it’s between 5% and 40% and leaving it alone if fragmentation is below 5% and index which are less then 100 Pages .
You're going to have to rebuild at some point. Index fragmentation can be a serious performance issue. Ignoring it won't make it go away. You need to find a slow period and schedule the rebuilds. Maybe do only one or two at a time, but you're going to have to do them.