I'm not clear on whether you have a machine to do piecing on or if you need that, too? Or if you have that and are just looking for a machine to do quilting on?
I have a sitdown Tiara for quilting and I love it. I don't have a problem spray basting or moving the quilt on the table with a suspension system, so it works great for me.
I was convinced I was going to buy a long arm and I rented time on one many times and tried to use it and just couldn't get the hang of it, so be sure to try one out before you make any decisions. In fact, be sure to give any machine a good trial before you make any decisions, if at all possible. Don't be afraid to ask for a deal or add ons from a retailer.
I agree with making a list of things you absolutely need, things you'd like and things you can do without. Also consider buying used...It can save you money and allow you to buy a better machine than you might be able to afford new. Be sure that you have tech support in your area for whatever machine you choose.
Take your time and watch out for on-line deals from legit companies, especially right now.
Let us know what you decide!
Watson