I've always been a fan of subscriptions bots here on steemit and I think they are good for the platform.
It's a model I've very fond of here on steemit. This is when you pay some fee in advance to have ongoing votes on your posts. There are quite a few here on steemit and I'll offer a list and review at the end of the this post. Of course I'll also disclose my own conflict of interest right upfront that I run a subscription bot 
I'm not going to spend much time talking about or bashing bit-bots I think that's been debated extensively already, they certainly have there issues and perhaps no bots at all would be best, but that's for another discussion.
I think these services have many benefits over the traditional bid-bots.
Screening members
I think this is the first benefit in that usually there is a process with these services to apply and that usually includes screening members to eliminate any spammers or plagiarizers. I do know that many bid-bots create and share blacklists and that helps, but I know others don't and it's much easier to slip through the cracks.
Creating community and curating content
I think this is an important aspect of steemit to create community and connections between people. Most of these bots have a discord channel where people can meet and connect and often friendships are made. Many of these bots also have daily or weekly content curation when they share some of the posts and/or resteem some posts to help promote good content on steemit.
Increase posting
By subscribing to these services often people are more motivated to post daily or at least on a regular basis to be sure to reap the maximum benefit. Of course this can also be a double edged sword as some people may resort to "shit posting" just to maximize the reward.
Rewarding creators
Of course this also happens with bid-bots, but they of course help reward creators with larger post rewards which of course can also be motivating and keep people engaged with the platform.
Simplicity
This is one of my favorites, is that it's just simpler. You just send you payments and the vote starts rolling in on your posts, no need to drop links anywhere or send any additional wallet transactions. It can save you some time and hassles on a daily basis.
Putting you SP to better use
Many of the subscription bots accept delegations of SP as the subscription fees. I think this of course is the best way to subscribe and will net you the biggest rewards. When paying STEEM/SBD for subscriptions you will likely get lower rewards over the term and you of course have to recoup this investment, but when your delegating SP you are getting much larger rewards in return. In fact delegating to these services and getting a vote in return is much more profitable then delegating SP to bid-bots and getting a portion of their profits.
Comparison of Services
I know a lot of people may not even be aware that these exists, so I'm going to present the one I've aware of here in a chart with a bit of details. Otherwise I would suggest investigating further if you decide to join.
| Bot and most recent post | Logo | Discord channel | Subscription method | Total current SP | Curation | Tiers |
|---|---|---|---|---|---|---|
| STAX Link | https://steemitimages.com/0x0/https://ipfs.busy.org/ipfs/QmQqf9ebgMQbmDYNX7diTuEpumbvuLGTvjFFZKMcKb73Cm | https://discord.gg/C5scqRP | Delegation only | 131,277SP | Yes | Custom (delegate any amount between 50SP-5000SP |
Qurator  Link | https://discord.gg/pJtWp57 | Payment for lower tiers, Delegation for Higher | 120000SP | Yes | Yes-11 different tiers | |
KiwiBot  Link |  | https://discord.gg/WBVTmQ6 | Payment or delegation | 5,079SP | No | 1 tier |
IncinCommunityBot  LINK |  | https://discord.gg/VmR96ba | Payment or delegation | 3,039SP | No | 3 Tiers |
Jumbot  Link |  | https://discord.gg/kxSFrGB | Payment or delegation | 10,587SP | Yes | 3 Tiers |
Moonbot  Link |  | https://discord.gg/GNQxMaP | Payment | 4,597SP | No | 1 Tier |
Chart optimized for viewing and posted with busy.org (not sure why it won't scroll on steemit.com)