Hello All.
I am new to card stock modeling, this website, and really even Role Playing Games (With only a year and a half experience under my belt). I have played wargames in the past, but I have practically abandoned them after discovering the more in depth Role Playing Games. Since my first introduction to Dungeons and Dragons, I have begun to take a liking to the Game Master’s position as I like to be the one who designs the basic story and my favorite part which is world building. However I have recently hit a rather critical impasse and although I think I may have already spotted a decent solution I figured that I would try the forums first to get some advice from others.
My problem is not so much a snag in world building (which I think I have down fairly well), but rather game mechanics. The setting is my own custom setting and was originally destined to be set in the d20 system (d20 modern with elements of d20 future to be exact). However as I worked on the world and the details of the campaign, I have begun to doubt that the d20 system will meet my needs for this particular setting. In short I am not sure what system to use. I mostly have world details finished so I have not yet done most of the horrid ‘statistics’ part of it yet. I have however outlined my particular needs in a system and they are as follows.
• Something rather universal not campaign specific as it will be adapted to my own custom campaign setting.
• Something that can handle modern technology, future technology, and magic/psionic systems coexisting in the same world. Players will be human and slightly above average, but not super humans.
• Something with good vehicle rules since my world currently has a LOT of vehicles in it.
• Something classless. I have played D&D long enough to hate classes and that is why I liked d20 modern since classes were more customizable. Then I discovered that other systems did indeed exist (this also shattered the world view of many of my friends who played D&D) and that a good number of them did not use classes at all. I have grown to like this approach.
• Something fairly simple. My players are far too lazy to even read the Player’s Handbook and would probably crawl into a fetal position and weep if they saw the Hero System book.
• Something that can handle fairly large battles.
Kind of a hefty order I know and I know what you are probably thinking “Why don’t you just stick to d20 modern since that is what your world was originally built for?”
There are three reasons I am thinking about abandoning d20.
1: I hate classes. The majority of my characters are hard to define in just one class. This results in a horrid multi-class monstrosity that takes hours to make into something decent.
2: Making opponents is easier when you can balance them using points. I hate predefined monsters that the d20 guide gives you and I often just make my own. Though I have gotten better at it, it is still a painstakingly complex and long process and it takes forever to readjust all those stats trying to get the CR to a predefined target. I consider the Challenge Rating system the least documented part of the d20 system. They might just as well name it the ‘use only stuff in the monster manual’ rule.
3: Vehicle rules are too complex when on a larger scale. In d20 modern the M1A2 Abrams tank cannon does 10d12 damage. I don’t have 10d12 dice and dice rolling programs would be nice if I had a laptop to bring to a game session (my laptop is currently KIA). I can add these up manually, but that takes time. What is even worse is that many of the vehicles that I have given d20 statistics to have weapons much larger than 10d12 (25d12 twin linked 200mm railguns). I did run a test battle with 9 attack bikes vs. one super heavy tank and I was so bogged down in details and statistics that it quickly became apparent to me that a simpler system was needed.

So far I have done a fair amount of research on various systems and I have come up with the following systems that may be useful.
Savage Worlds: Number one on my list and my current leaning. It is simple, classless, has simple vehicle rules, and can handle larger battles. Definitely my top pick currently, but I have not tried it and would like some second opinions.
GURPS: Many swear by this system and I can see its appeal. I have looked at the ‘lite’ version and it looks okay. However, others say that it is too complicated when you get further into the main rules.
White Wolf/Storytelling System: I have met many devoted and rabid fans of the White Wolf systems. My biggest problem with this system is the fact that I did not see many vehicle rules and it seems to be rather campaign specific.
The Tri-Stat system also looked very comprehensive, however once again vehicles are practically neglected.
I would probably never use the Hero System except to scare my players into submission when they become rebellious. “Are you going to cooperate or do I need to make you change your character to the Hero System?”

I would like some opinions from veteran players on what might be best system to use in my case. Thank you in advance.

This will come as no surprise to anyone but I recommend Savage Worlds as well. The new rulebook is only $10, which will be available soon. They were available at Origins and GenCon. The Test Drive rules are free but the newest book changed things slightly. The tabletop vehicle rules are incredibly good and the system really excels as a straight miniatures game as well as an RPG.
I think you'll find a lot more freedom with SW over d20.

An official run down of the Spycraft calibers, taken from the living Spycraft site....

Caliber I -- We just need a baby sitter.
Caliber II -- Not quite a cake walk, some danger involved.
Caliber III -- Dangerous mission.
Caliber IV -- Suspect major threat to large population base or other large ramifications.
Caliber V -- Known major threat to entire foundation of civilization.

The Auld Grump, I don't think I have ever run a caliber I or caliber V mission....