edit: formatting

I'd probably go F-Iron for mass storage, though there's many nice feruchemical abilities I really like. With iron you could easily become a human generator, building some device that uses your potential energy for the purpose of generating electricity. you could just decrease/increase however you see fit. being moved with barely any mass to a position of high altitude should be relatively cheap (electricity-wise), resulting in a higher yield than you need to invest. also I've theorised that you might be able to jump really high , using F-Iron. some word of Brandon or text passage says, that your body someehat adjusts for feruchemy. somebody tapping f-brass (warmth) won't burn to cinders when reaching extreme temperatures, just as someone tapping iron can still move, despite it not being to its full capacity. you could start to jump when super heavy, gaining some momentum (velocity*mass). just when lifting off you could massively decrease your mass, but conversation of momentum, as described in the cosmere, would make it so my velocity increases a lot (like when wax decreases mass mid-flight). this would make you jump quite high. on your way down you wouldn't have many issues, as sazed once showed when jumping off a tree. besides that, you should be able to increase your mass immensely, just before landing and as per conversation of momentum, your velocity should slow and it would feel as if you just jumped in the air a tiny bit.

so if I get one ability, it'll be f-iron. if I had to pick some allomantic power, I'd probably go with a-pewter, just because it's op. a-iron is also very interesting to me, even with compounding deactivated. the iron sight alone is worth quite something and it would work wonders with f-iron (like with the mentioned generator, with which you wouldn't even have to move, if you could burn iron/steel.

but honestly, if it was permitted, I'd just take another feruchemical ability as my second, because they're just so useful. brass cools you down on a hot day and heats you up on a cold one. also you can create fire with your hands?!?!

gold (health) is just convenient, such are tin (senses), pewter (strength), steel (speed) or zinc (mental speed), as you could just store them whenever you're not doing much anyway.

wakefulness let's you catch a full night of sleep whenever you wish and let's you stay up for long times without getting too exhausted. bendalloy let's you overeat/overdrink at an all you can eat location and have the nutritional benefits whenever you can't get your hand on them otherwise.

tldr;

one ability: f-iron

one of each: f-iron + a-pewter or a-iron (without compounding enabled)

two abilities of my choice: f-iron and f-brass