Much as I would like to, I am not going to trash Oracle. It is a fine product and obviously it gets the job done well or it would not be the market leader. So, I will just tout some of the features and attributes of Informix that have caused its users to become fanatics over the years:

• Great OLTP performance. During the ’90s database wars, Informix and Oracle battled for the “Best” OLTP performance label. Informix today is significantly faster than the versions available then. Note that to my knowledge Informix has never lost a comparative benchmark with Oracle, Sybase, SQL Server, or anything else based on performance.
• Industry leading replication technologies (multiple):
• Hierarchical Data Replication Secondary Server
  A single read-only or read-write secondary server with its own storage is kept up with the primary in synchronous, near-synchronous, or asynchronous mode. Can take over as primary on primary failure
• Shared Disk Secondary Server
  Similar in concept to Oracle RAC, multiple SDS secondaries can share disk with the primary in read-only or read-write mode. SDS tends to scale to a larger number of secondaries than RAC and new SDS servers can be spun up in seconds to handle unusual transaction or query load. Any SDS secondary can take over as primary if the primary fails.
• Remote Secondary Server
  Multiple RSS read-only or read-write secondary servers with their own storage are kept in sync with the primary near-synchronously. RSS secondaries can also be maintained with a time delay as a foil against fumble finger data damage. RSS secondaries can be promoted to HDR status if needed to replace a crashed or promoted HDR secondary.
• Enterprise Replication
  Flexible log shipping replication which can be multi-directional, data gathering from partial servers to a central database, data scattering from a central database to remote full or partial servers, or any other configuration.
• Smart Triggers
  Applications can register to receive notice of changes in data rows. This is different from Change Data Capture (also supported) in that data changes are not send, only notification of a change.
• JSON/BSON data supported as Class I data types.
• MongoDB Wire Listener protocol support.
• REST protocol listener support.
• GeoSpatial data support.
• Timeseries data support.
• Efficient User Defined data Types (UDTs). Several Informix data types are implemented as UDTs and perform as well as similarly sized built-in types.
• Virtual Table and Virtual Index interface APIs allow you to extend the functionality of Informix to support external data sources and new kinds of tables and indexes.
• Support for distributed ACID compliant database including sharding support.
• In-place table alter.
• Support for automated compressed tables and indexes.
• Support for encryption at rest for all user data spaces.
• Vertically scaleable from a single core Raspberry Pi to super computers sporting hundreds of processors.
• Highly embedable with excellent autonomic tuning support.
• Configurable disk footprint and feature installation.
• Informix Warehouse Accelerator - This is an in-memory, highly compressed, columnar query accelerator capable of accelerating queries several hundred times faster than the base Informix engine. Intended for complex data warehouse style queries and massive data sets, this can distribute a data mart across many nodes when needed. It has the unique capability to process warehouse style queries against a near real-time copy of your operational OLTP database without affecting OLTP performance.
• Several Editions:
• Developer’s Edition - fully featured, resource limited, free for development and learning only.
• Innovator-C Edition - feature and resource limited, free for any purpose except to redistribute (distribution licenses are available for reasonable fees) including for production use.
• Express Edition - feature and resource limited (but more generous than Innovator-C) it is intended for in-house or independent application developers looking to embed a database engine within the application itself to support the application’s functionality.
• Workgroup Edition - Intended for midsize companies or departmental servers in an enterprise deployment. Fewer limitations than Express.
• Enterprise Edition - As the name implies, this is a full featured enterprise class edition with no resource limits. There are a small number of add-on features not included in the base Enterprise license.
• Advanced Enterprise Edition - Includes both Storage Optimization (compression) and the Informix Warehouse Accelerator described above.
• Ability to upgrade a cluster of servers without any downtime.
• Ability to build a server cluster from heterogeneous server technologies incorporating servers using different hardware processors and operating systems working together.
• Industry leading reliability and uptime. A 5-nines year for an Informix installation is a disappointment. Informix instances have been known to remain online serving clients uninterrupted for 10 years and more.
• Unsurpassed user community support.
• Highly active user group (International Informix Users Group - www.iiug.org).