The decision of subwoofers versus speakers for bass has always been on the battling radar for decades and really still is up for debate. I think it’s all a matter of opinion on what you as an individual are looking for. I’ll just jump into the debate instead of of just sitting here babbling.
First of all, audio speakers bass can only get so loud. It really depends on how much bass you want. If your looking to shake your rear view mirror and get people’s heads turning than speaker bass is not for you. There is a reason subwoofers were made, and that is to push low levels of bass.
The subwoofer setup will cost more and there is no way around that. You have to have someone run the wires under the carpet and from the battery to the amplifier. Wires from the the back of the deck to the amplifier. Then wires from the amplifier to a ground on your car. It really is not that complicated, but some find it very complicated.
Installing new speakers really just amounts to taking off certain panels and unplugging wires and installing the new speaker and re-hooking up wires. THAT IS, if there is not a amplifier pushing the speakers. And if there is a car amplifier pushing the speakers, you might as well just re-do it all.. subwoofers and speakers all in the same idea.
I know its a bit complicated.. but which ever way you take there will be some expenses you cant get around and it will be some hassle. To get GOOD sounding bass is never cheap unless you know the right person to do it.
So to give you nothing but my complete opinion, I would “if it was me” get a descent quality of speakers and just get descent subwoofers installed with their own separate amplifier. It will be the easiest for the cost. Because most speakers that put out some bass need an amplifier and by that time, you might as well just do the subwoofer thing.. that way you can get as much bass as you need for your desire.