I think it's too early to talk about security and efficiency of Solana's Proof-of-History consensus (it creates a historical record that proves that an event has occurred at a specific moment in time) which works with Proof-of-Stake mechanism and its additional layers (protocols) but some obvious things are written in a White Paper.
Here's an excerpt from white paper:
The combination of Proof-of-Replication and Proof-of-History provides a defense against forgery of the ledger with respect to time and storage. The protocol is analyzed on a 1 Gbps network, and this paper shows that throughput up to 710,000 transactions per second is possible with todays hardware. The average transaction fee in Solana blockchain is $0.00025.
As you know, when Hydra will be implemented in Cardano, the network can process up to 1,000,000 of transactions per second. The average fee for a transaction in Cardano is approximately 0.15 ADA.
Both, Solana and Cardano support smart contracts. Both networks are energy-efficient (it's hard to say which one consumes less energy). Both are fully decentralized, and both are rapidly developing.
P.S.
And a few words about network's reliability. Today Bloomberg reported at 6:40 p.m.: Solana’s blockchain network has stopped processing transactions.