Define "good"...
SEAL:
- very fast on general purpose CPUs
- uses a lots of RAM
- Proprietary in nature
- not as cryptoanalyzed by the security community as other ciphers
3DES:
- very fast only on dedicated hardware
- does not use as much RAM as SEAL
- Has been proven to be reliable in many years of service by many experts.
Between these two - take in the account any data security standards that you have to follow, type of data being transferred, your hardware and the throughput that you will need.
If you are willing to live on the bleeding edge - SEAL will be fine. If you want to be conservative - 3DES.
IMHO, you should skip both and use AES if possible for the following reasons:
1. SEAL is relatively unknown. It very well may be the best thing since sliced bread, but I would not put any state secrets on it until it is proven.
2. 3DES is fairly old and slow. It has been partially broken to give "only" 112 bits of security (still plenty)
AES:
- Fast on general purpose CPUs
- Uses moderate amount of RAM
- has been analyzed, is being used by the .gov and is a new standard.
