Both can protect your capital, but they differ in who backs them, how easily you can get your money out, and what they promise. A Singapore Savings Bond is backed by the Government and can be redeemed in any month without penalty. An endowment plan locks your money in for its term, with a guaranteed part and sometimes a non-guaranteed bonus on top.
Who guarantees what
A Singapore Savings Bond (SSB) has its principal and every step-up in interest guaranteed by the Government. An endowment plan's guaranteed part is guaranteed by the insurer under the policy terms. The two are different promises from different parties, and it is worth reading what the policy actually guarantees.
Getting your money out
An SSB can be redeemed in any month without penalty. An endowment plan runs for a fixed term, and ending it early pays the surrender value, which is usually below what you have paid in the early years. If you might need the money, this difference matters more than the headline rate.
Returns you can compare
An SSB states an interest schedule, and the 10-year average is a comparable yearly figure. An endowment plan often shows a guaranteed value plus an illustrated, non-guaranteed bonus. The illustrated figure is an assumption about the insurer's fund, so to compare like with like, use the yearly return on what you actually pay, which the analyser works out from your illustration.
What a comparison cannot capture
An endowment plan may include insurance cover or other benefits that an SSB does not, and an SSB may be easier to adjust as your needs change. Neither is better in general; it depends on the goal and the time horizon.