I'd suggest
Intercasino as they have monthly matching bonuses, typically of $50 to $100 (September is $90). So, if you put in $90, you'd have $180 to play with. There'd be a minimum betting requirement to cash out the bonus (15 or 20x the bonus). But, given a good blackjack player only gives the house a 1% advantage, that tends to you an overall advantage.
Intercasino is also one of the oldest and most popular online casinos, so one can be assured of getting paid if one cashes out (I play there myself).