Which one should I pick for a new project?

Neither repository is a suitable choice for a new project:

liyifeng1994/ssm: This is a teaching/learning project for SSM (Spring + SpringMVC + MyBatis) integration, not a production framework. Per the RepoPilot verdict: WAIT — Stale — last commit 3y ago. The repository is explicitly designed as educational material ("手把手教你整合最优雅SSM框架" = "hands-on guide to integrating SSM framework") for developers new to Spring. Modern alternatives like Spring Boot and Spring Cloud are recommended in the README itself [README.md:L4-L6].

reactivex/rxandroid: This is a legitimate, active reactive programming library for Android. However, it's not a project starter—it's a dependency you'd add to an Android project. It provides scheduling and threading utilities for RxJava on Android, specifically AndroidSchedulers.mainThread() for observing on the main thread [sample-app/src/main/java/io/reactivex/rxjava3/android/samples/MainActivity.java:L29-L80].

For a new project:

• If building an Android app, evaluate whether you need reactive programming. If so, add reactivex/rxandroid as a dependency alongside RxJava.
• If building a Java web application, use Spring Boot (not SSM)—the SSM pattern is dated. The liyifeng1994/ssm repository itself acknowledges this by recommending learners graduate to Spring Boot and Spring Cloud.

FOLLOW_UPS:

• What type of application are you building?
• Do you need reactive programming for your use case?
• Are you learning Spring for the first time?