They’re both good games that are played with certain sets of rules. However, when we’re talking about three card poker so the house edge there is 5 to 10 size comparing to blackjack’s house edge. In general, it is typically for blackjack to have 0.5% for the house, 3% to 5% for three-card poker.
In three-card poker mathematical counting won’t help you to turn the edge on your side. In blackjack, it is quite possible.
To sum up, it can be considered as something between usual poker and blackjack.