I would say TG overall. This time you can solve many of your problems with raw force, which is really nice for non-stealth characters

No, really, the real reason is that long rebuilding "quest", after which you really feel you have deserved your position as a leader. DB comes second, because of that ultimate job you are doing to earn your position.
In College questline, the story of "The Staff of Magnus" quest is nice. What is wrong with this questline, is that you become an arch-mage way too early and easily. I would done the same to both College and Companions as it is with TG. College already have good quests to be used, e.g. you should do at least three out of five ritual quests before being nominated as an arch-mage (assuming that high level mages vote for their arch-mage, you would gain majority), or it could well be that you would need to do them all before nomination. As you can gain arch-mage position without any sort of magical skills, you know, it is somehow embarrassing to ask the master wizards to teach their arch-mage

Similarly, you gain your leadership of Companions too quickly, it would well involve some TG-like quests before your position is recognized.
Bards... I was so much hoping that my character would learn to play instruments, I even carried a flute with me a long time with my first character... The disappointment was much too deep to ever come back to that guild...
FuzzyMage wrote:With some of the assignments, you just couldn't get a kill and escape. (For example, the one where you off the bride in the wedding - no matter what I tried, following the examples and suggestions from the wiki, I could not do it without getting caught.
I have had no problems with this. What you need is high enough sneak skill. Go to the top of walls, and shoot an arrow from the corner. Stay in sneaking mode until the red dots disappear, and you can fast-travel away. If you go to get the unique loot (wedding dress and such), you can do it without fighting after the red dots have disappeared; but keep in mind that the lizard who has been sent to watch your back follows you and start fighting with guests, if you spend too much time with them
FuzzyMage wrote:The invisibility potions simply didn't do the trick, which [&@%!] me off to no end. What's the use of a potion if it doesn't work?)
Invisibility is a little bit difficult in Skyrim. I don't know the details, but NPCs detect you based on your visible and auditible "distractions", and Invisibility only removes you to be seen (that is, you can sneak in daylight). If anyone hears you, or if you touch someone, you are detected and Invisibility does not protect you anymore. Similar to Oblivion, Invisibility effect is cancelled if you do anything other than move, which is why it does not protect you when assassinating people. Basically, you would need to combine Invisibility and Muffle, and I am not sure if you will still need high sneaking skill to remain undetected under difficult conditions.
FuzzyMage wrote:People, the mark of a successful assassin is killing your target and getting away with it.
Absolutely. I'm pretty sure I have been able to complete DB questline without any bounty, and without any more-than-usual gears or tactics.
FuzzyMage wrote:The next character I use (this was my first, and I can tell you a mage isn't the best type of character to use for the DB, heh!) is just gonna destroy the bloody thing.
Yes, mage is not the best one... I have trusted on archery in both Oblivion and Skyrim DB quests, it is much easier (i.e. requires lower Sneak skill) to sneak to a shooting distance than sneaking to stabbing distance.