I have been receiving quotes to replace my outside and inside unit here in South Florida. I want to get a 3.5 ton 15 seer unit. I have gotten quotes from Trane (with the clean effects filter - does anyone know if it is worth it?), the carrier infinity and now a Payne variable speed - both the trane and the payne will get me 10 years warranties on all parts and the Payne will give me 5 years labor too -
Please let me know if anyone has any answers for me - of course money is a consideration, I plan on staying in this house for a while and would like to make the best investment possible.

Does the air filtration system really work and is it worth the extra $$$$$ -

The air filtration works well.

You need to pick the contractor by ability not price. The install is much more important than the equipment. Get the best and longest warranty for both parts and labor especially since that variable speed motor can cost 800.00 plus labor to replace. I do not care for variable sped motors because of the high replacement costs. Also make sure it is a factory warranty. This way if the contractor goes out of business you can contact the manufacturer for repairs.

Is it worth it to go for the air filtertration?

It all depends upon your situation. If you have health problems it will help. If not then do not worry about it.

I just had a Trane unit installed in South Florida by AAA Modern Air. They were reasonable, did a clean job, and offer a 2 year parts and labor warranty upon install. Most companies only give 1 year. AAAmodernair.com