There are 2 popular ways to enchant:
1. Use the some option. It is believed that there are hidden PG for enchants, thus resulting in successive successes or fails. This should be the best/least expensive way to enchant. Only down side is some people will lose all their stats on an item if extremely unlucky. Usually stop enchanting for the day once u have the first fail.
2. Use the bountiful option. In the version 140 update, fails on bountiful option no longer result in minus stats. Thus given enough gems, u can always max out enchants. the down side is, this cost way way too much. Also given the 140 update, bountiful can no longer give +6,+7 stats, it's range is reduced to [0,+5]. Currently our 130 version should be [-2.+7].
Enchanting Facts and Tips - Orochi