Followliker is fast and frequently updated but (I suppose) because it is the most popular bot it seems to have the most effort from IG in suppressing likes and follows and other actions that might provoke a ban or block. If you keep up on the news related to that in the forums here and elsewhere and put effort into working around and within those limits it may still be the best program to use.
Other popular services like Instajool, Gramdominator, and cloud-only or cloud-linked services are more user-friendly and portable (able for your clients to log into to better know what you are doing) but are usually more limited in features and may not be able to be set to run as fast as Followlliker. In general, the more features the harder the program may be to configure but the more powerful it may be. If you are simply trying to maintain and add a little growth to an already popular account that extra "power" that comes with dozens of settings and sub-menus may not be needed, and may not offset the conveinence and portability of a cloud-based service.
Most of your efforts should focus on getting good content (posts) and lists of contacts to follow/like/message on your client's behalf. That really can't be overemphasized. Your choice of your process for collecting, filtering, sorting, and planning your runs of follows/likes/DMs/etc may more determine what program(s) you use than sheer ease use or the cost of licensing those programs. The better the content, the more "organic" the growth will become -- the more the product will sell itself and grow followers and sales on its own -- and the faster you will be able to run a bot if you choose to do that.
Too many marketers are still spamming accounts who they have no reason to believe might be interested in the posts related to the product or service being spammed, provoking social media platforms to crack down on third-party marketing programs like Followliker. The more spammers who try to market fidget spinners and porn to all 104 million followers of Taylor Swift's IG account, the more difficult a marketers job is going to become, outside of simply paying IG to run ads for you. If the only option for marketng on IG really becomes ads sold by IG, third-party efforts like Followliker and many marketers as well will have to go out of business.
