When I began model building again back around 2000, after about a 15 year break from it following high school, I concentrated strictly on armor. I got the buzz for it thanks to all the WW2 tank-centric shows that were on History Channel, back when they still did actual historical subjects and not the non-stop brain-dead nonsense on UFOs, lost Atlantis, and Hollow Earth type of programming they've been doing for far too long.
When I moved a couple of times in 2003 and 07 to homes with more space I added aircraft building into the mix. And some sci-fi as well. I've made some attempts at warships but I find it to be problematic - 1/700 scale is just too small for my clumsy fingers & weak eyes, 1/350 is just too expensive, and the photo-ech sets of any scale for the ships to me are just a nightmare to deal with. As such I've pretty much stuck consistently with just armor & aircraft. I have a couple of ships on the go right now but they'll probably be my last ones due to the aforementioned issues. I'll gladly forego the ships though to hopefully do more Star Wars, Star Trek, BSG, and other sci-fi subjects instead.
I would really like to give a go at some car models, like the Impala from Supernatural or the Plymouth Fury from Christine. My only hesitation is that AMT makes the majority of these kits and, as per too many of my other posts here lately, I am not fond at all of the quality of their kits due to the burnt-out molds they've been using for decades and refuse to update. I just don't want to spend money on a kit where there won't be a single decent fitting part in the entire box. I know from other builders that the Tamiya car & motorbike kits are absolutely great. But my preferences are to do classic North American vehicles, not the Japanese rice rockets, so it's fairly unlikely I'll ever do one of the Tamiya subjects.
Other than that, when more money is available, I'd really like to do some Maschine Krieger. And I've heard that some of the Warhammer 40K kits are decent as well. I can't say I'm too fond of Gundam or the other ones based directly on Japanese cartoons. My heart's fondest wish insttead would be for a good reliable company to produce kits based on the classic Battletech wargame, in a decent consistent scale like 1/48 or 1/35. Other than that I'd like to tackle a dinosaur model, but those are few and far between in terms of availability. I think that it might be a better option to go buy the best plastic or vinyl dinosaur toy instead and use full range of basic model painting & weathering methods to try to make something decent out of it.
It would be nice to have better computer skills and enough money to by a 3D plastic printer or a resin printer. That way any one of us could just buy the plans online and make our own kits that none of the manufactures produce. And any of the smarter & more-skilled fellows here with some decent design tech skills could probably bypass buying plans altogether and just create it themselves instead. I'm too long in the tooth though and get out of sorts too quickly by newer technology to ever try something that complicated myself.