The qualities of the trick that you find disheartening are actually advantages in my routine, and you can use them to create a blockbuster effect. This fifteen dollar trick is now one of my favorite things to perform.
I patter about how important it is for the spectator to be absolutely sure that I'm not in any way influencing his/her choice, despite the numerous ways that I may do so. Then, I spend a large amount of time actually describing the subtle ways I might be trying to nudge him in a certain direction. For example, the difference in card stock might be a way of getting him to choose that card. The fact that 3 of the 4 cards are shaded in primary black/white/red colors, while one is green might be a tactic. The fact that three of the characters are wielding guns while one is hidden might be a factor. I mention one of the characters as my personal favorite - maybe there's a nudge. I mention one of the actor's making a comeback with this popular role, and that later weighs on their mind. I mention one of the actor's as possibly the greatest actor of his generation - that may have an effect on their decision. I place one of the cards closest to them. Another card I gently touched. I remind them that in the actual films depicted, only one character actually survives - maybe this is important. The point is, I bombard them with so much meaningful(?) information, that the ulitmate meaninglessness(!) is heightened, and the humor of their eventual choice is accented. By the time they make up their mind - they're practically sweating, because they've attached an artificial importance to the proceedings - they don't want to mess things up! It's very funny to watch and I get as much as ten entertaining minutes from this fifteen dollar trick. As for the one card being a bit bigger - that actually helps in the handling. Place it on the bottom of the cards you will be pulling out of the envelope (the remaining out is tucked in way beneath it), and it makes pulling out the four cards very easy - there's no fumbling. I simply open the flap, grab the biggest card, and the other three "visible" ones ride out on top of it. It happens so quickly as I patter that nobody (and I mean nobody, in countless performances) has ever noticed the miniscule flash of white as I use the cards themselves to close the flap. There is no need to get a bigger envelope. In fact, I still use the cheap, thin, ugly brown envelope that came with the trick. It's worn and ragged, and actually adds personality to this quirky trick. As for what you termed the weakest out, it's perfectly fine, provided you forget the instruction to write the words in small letters as you would a real letter - instead boldly print them on the whole front side - make a statement! As for guys always choosing Taxi Driver - it's easy to subvert by simply mentioning that most people choose Taxi Driver! In fact, it's fun and easy to actually lead people to whatever choice you want - if they don't pick your favorite right off the bat, then tell them you're going to give them one (and only one) chance to change their mind; after that they're forever locked. This simple ruse works in my favor, and they usually switch to a better choice. Granted, my personality and experience helps me tremendously in this effect, but I know that by injecting a bit of these tips into your unique handling, you'll get better results, and more importantly, enjoy the effect much more than you currently do. If you give it a try, you'll be rewarded. If you don't - well, that's just one less magician doing a trick that I adore. Best of luck!