As far as acid content is concerned, peaches are in the middle of the spectrum. Although they may not be quite as acidic as limes or lemons, they still have a somewhat significant acidic content and should therefore be eaten in moderation by those who have problems with acid reflux.
If you have a problem with acid reflux/heartburn, you will want to limit the amount of peaches you consume in a single sitting.
While there are definitely certain fruits that have a much higher acidic content than peaches, they should still be avoided by those who suffer from the problem of acid reflux.