I've tried both - we used smart nappies when Leyla was born and I really liked them, but they're very boring! Also because they have quite a narrow gusset bit that the insert goes into, they're quite hard to boost without the nappy getting very bulky so not great once your LO starts weeing more. They would never last for Leyla overnight now she's bigger.
I'm assuming you're looking at the one-size pocket BGs (like the ones on the Mothercare website)... they're much easier to add extra absorbancy to than the smart nappies. A big advantage of them is that they're one-size so will last till potty training, whereas you'll have to buy more smart nappies as you go along. With pocket nappies though, you can't reuse the outer and just change the inner bit when LO wees, you have to change the whole thing.
A good compromise between the two is BumGenius Flips - they're basically an outer with an insert that goes into them. They don't have a a narrow gusset like the SNs so you can add extra boosters if you need to as LO grows; they're birth-to-potty; they come in three nice colours so far with the full range of colours to come soon-ish; you can just change the insert if the nappy is just wet and you can also get disposable inserts like you can for the smart nappies.
Not all nappies suit every baby though, so I would buy just one of each to try first. You can buy each of those singly and if you posted a Wanted add in the Cloth Swap and Sell section, I bet somebody would sell you them preloved too.