Well, I will give you my opinion.
That's all I can offer.
I never liked convertibles:
1) Yeah, security is an issue.
2) Putting up and down the top (I assume it gets old after a while)
3) Burning hot seats in the summertime. Sun burning your neck.
4) Top down so you have to crank up radio to hear thus soon going deaf
5) If you run at the dragstrip, if you do 13.99 or better you have to have a friggging roll cage (at least 5-point), whereas with a hardtop you have to get to 11.99 or quicker b4 you need a 5-point cage.
6) Verts are heavier
7) More crap to maintain (motors for top to go up and down, the vinyl top itself b/c if not it will deteriorate faster than a hardtop, etc)
8) A little less space in back seats
9) Hardtops just look better/cleaner, IMO
10) Hardtops are less $$$
Concerning manual or auto. Autos are just less troublesome, practically speaking. Think about it. You're sitting at a light trying to talk to your girl while sipping a sodee pop and the light changes. Now you gotta find your cup holder and shift through all the gears while talking to your girl. Everyday, day in day out whenever you drive the car, you'll be pressing a clutch and shifting through gears... when it's wet also, you gotta be more careful b/c they are easier to spin out during acceleration in the 1rst and 2nd gears. Another scenario, you come to a light and this punk in his Honda CRX V-tech Type R SiR GT-R (
) is trying to show off to his preteen girl how cool he is by revving you and challenging your stang. Light turns you launch in 1rst, come out grab second and you got him by a half of car length thinking "BYE BYE," but right when you go to shift into 3rd, OOPS, you slam right into the space b/t 1rst and 3rd and he fly's past you to the next traffic light, now you're too embarassed and his little girl friend is laughing at you and punk kid now thinks he's fast and furious.
Just something for you to think about.
BUT, if you an auto, the more you you see manuals out there, hear them, and understand their potential, you will probably want one. They're fun if you have them in a car like a stock mustang and super fun if you're driving a moderately to highly modded stang.
With all this I've probably reopened up a can of "Manuals are better than Autos" worms, but I can tell you what, you'll never hear me say while driving my '79 "Oh wait a minute, less race again, I missed *insert gear here* gear....
If I were you, I'd get a manual (just get use to it) hardtop GT (like Blue00GTs mustang-- that is one nice stang).
GLad you have the sense to get a V8...good for ya
IN anything though, spend a lot of time (perhaps a few weeks to a month) and do the research. Don't rush things. Consider stuff like future mods and how they will fit on your new car b/c trust me, the mod bug will soon bite you and you cannot escape it's grasp. MMMMMuuuuwwwwwwwwwaaaaahh ha ha aha ah ha ahaha ha.