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Regarding the boots it depends how you have narrowed down your search. If you have been to a boot fitter and he has told you that a full tilt is the best possible boot for you, then get which ever there all the same and you can get differnt tounges. If you have just looked online and decided you like those the best, do your feet a favour and go get actually fitted and get the boot that fits the best. You dont need Full tilts or SPK's to ride the park, get what fits you the best.
Regarding skis we would need more info to give any usefull advice.
There are a ton of park skis out there and they all slide on snow, metal, and other jibby materials. Some are stiffer than others, some are more buttery, some will perform better on the rest of the hill. This is personal preference.
As for boots, read the above, if you haven't actually, yknow, tried on a pair of these things you're basically wasting your money.
Most brands will make JR boots, the SPK Kaid is good if you have a wider foot. the X3 JR can be good for a narrow foot. Head make some good JR boots. Best bet is try to find a decent shop, no offence to your brother but he does not sound like he has been fitting boots long, and have the boot fitter asses your feet and properly measure you. Getting things like footbeds will help the fit of the boots, getting full custom may be too expensize if your still growing, but some ready made footbeds will be alot better then the standard insole.
Overall though, dont get a adult boot just yet, wait a couple more years, also remeber witha JR boot you will want to get JR bindings, but again these will be cheaper, and will still work on a adult ski if thats what you end up getting. Skis like the Armada Coda could be good, the Salomon Threat or look at some K2's. Afterbangs are pretty heavy so may not be best for you. but try them you might like them
Yeah anything like that will be good, there is really no point spending the extra money to get adult stuff, as chances are it will be too stiff and heavy for you. You could get a good JR set up for the price of just some adult skis, so in my opion that will be by far your best bet. Try to find a good shop with a good JR selection and have them help you pick out your perfect set up.
Good luck with it and ejoy your season