Or you could be sensible and avoid sign-up perks altogether (bonuses and such - they only tie your money down to the casino until you wager the entire amount many times over, pain in the ass, don't do it)
I see you are located in London? If that's the case you can only play at casinos that are licensed by the UKGC (United Kingdom Gambling Commission). In terms of "winning chance" it really doesn't matter where you play; you have as much chance of winning at VideoSlots as you do at Trada or BetAT or anywhere else for that matter. What DOES matter is your own expectations. Have a sift through the accredited list here, browse through the reviews and see what takes your fancy. Look at the pros and cons of each casino and make a decision.
I would strongly recommend a casino that pays out rapidly (as almost all the highest rated ones do).
Have a high quality scanned copy of photo ID ready, as well as a utility bill and proof of your payment method; front and back copies of a card with first 6 and last 4 digits visible, plus 3-digit code on the back censored, for example. If you win, and we hope you do, a lot of casinos will ask for these documents when you make your first withdrawal. It's best to have them ready just in case, or even preemptively send them on signing up to avoid later hassle.
Stick around Casinomeister, the members on here are a knowledgeable bunch and will help you out with anything you need. Welcome and good luck