I've been using the Martingale system in online roulette for about two years now. It's proven to be pretty reliable as long as you're careful not to get too greedy or bored.
When it comes to online casinos, I have a few that I particularly favor for roulette:
BetUS Casino - This one is great if you love the classic roulette experience. They offer different roulette versions, but I've found that their classic version fits well with my Martingale strategy. They also have a pretty decent welcome bonus - $3000, if you deposit at least $50. Roobet Casino - This one's a bit unique, as it features a 14-wheel roulette instead of the classic 37-wheel. The jackpot color yields a 14x return, which can be a refreshing change from the norm. Just ensure your strategy fits this variant before plunging in. Slots.lv Casino - If you're a fan of variety, this is the place for you. They offer hundreds of different roulette variations, which makes it a lot of fun to switch between the classic game and an entirely new version. It also helps keep things interesting if you find yourself getting bored with the traditional roulette format. They have a welcome bonus of $5000.Remember, always do a bit of your own research before signing up, as the casino landscape can change.