Hi, Toraso!
As Janet already asked, how much grill space do you need? Plus, what's your budget?
As for rectangular, well, that's a bit tricky. I think it would be a little tougher to clean a square cooker, especially in the corners - from my experience at least. With a round bottom gravity does most of the work when draining grease.
Also rectangular shape allows nowhere for the moisture to run and collect, therefore dripping on you food. Rectangular design is used mostly for upright, or vertical, smokers because the moisture is let out of the top via exhaust (like in mine
Dyna-Glo).
If the reason is that you want more cooking space, I'd go with
Weber Ranch grill. It's a serious thing, not a toy-ish grill and just have a look at this bad boy. Pic is from the internet, but it looks impressive.
I have two smaller ones (22" and 26"), it's more than enough for family gatherings/parties/donation events and such. Also easier to carry around + cheaper from
bbq to go.
If you have any additional details or questions - feel free to reply, I'd be glad to help.