I'm not sure if either of them will appreciate car rides. I've heard more people talking of their success keeping green iguanas as free-roam animals than savannah monitors. I assume that's what you meant by "chill in your room". I know that green iguanas require more specialized care than savannahs. Unfortunately, both are usually farmed and not truly captive bred. Buying either would contribute to an already huge problem. I guess somebody is going to buy them though...
I will warn you that you're going to be blasted if you go onto the green iguana forums saying that you want an iguana to go on car rides and chill with you. Honestly, if that is what you want in a lizard (a bud to take places and hang out with) I wouldn't consider either of those choices smart. I think you made the right choice when you got the bearded dragons. They are much more suited to things like that than the two species you are interested in.
If I may ask, what happened to your boa and python? If you have a habit of acquiring animals just to tire of them and give them away (or sell them), I definately do not reccomend an iguana or a savannah, as rescues are FILLED with them. If these animals died, maybe you aren't ready for the responsibility of harder to care for herps like iguanas and monitors.
Also, by your dielect, I must wonder about your age. While a lot of teens are able to handle the responsibility of a ball python or a bearded dragon, they shouldn't take on an iguana or monitor. They get too big, live too long, can be dangerous (seriously!), require too much room, too much money to care for them right, and the majority of them get discarded as soon as the teen moves out or goes to college, if not sooner.
If you decide you need one or the other, prepare to spend at least $100 on books to help you know what you're doing. Set aside at least $500 for an appropriate cage (that you will probably have to build yourself or have built for you), $150 for heating elements like pads and multiple lamps and bulbs, $40 for various supplements (those cheap-o ones aren't what you'll need), and then of course probably a lot more for a humidity gauges, thermometers, a gram scale to weigh your new pet on a weekly basis (weight loss is usually the first sign of a problem), an automatic thermostat to controll the cage temperature, substrate, cleaning supplies, food (which gets expensive for both of those animals), claw clippers, cage furniture, a first aid kit (both are dangerous animals), and so much more that I haven't even begun yet, but I'll stop.
If you are wanting a new lizard that will be content to just sit next to you, be petted (not necessarily picked up), and "chill out", I'd recommend a giant plated lizard. They are usually wild caught, but out of all the lizard species, they are more likely to be "tame". They still need everything I've described above, just on a somewhat smaller scale, and thus less expensive.
I've included a picture of my male, named Lizzy Butt.

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~Sara~
1.2 ball pythons (Scorpio, Dayzee, and Satan)
1.0 Black-lined plated lizard (Lizzy Butt)
0.1 Burmese Python (Pixil)
1.0 Pacman Frog (Pudge)
5.2 Pet Rats (Emo, Skye, Siam, Lilac, Manson, Spade, and Zilk)
1.1 Dogs (Ozzie and Mandy)
0.1 Cat (Isis)
0.0.1 Synodontis Catfish (Big Spotty Fish)
0.2 Convict Cichlids
0.0.2 Crayfish