Does anyone have experience with Tunnels and Trolls? If so, what's the difference between versions 5.5 and 7.0? Is one better than the other?

5.5 is 5.0 plus an extra add-on chunk including some "optional changes". It literally includes a direct exact reprint of 5.0.

5.0 Stats: STR, DEX, CON, IQ, LK, CHA; SPD optional. 3d6 each.
5.5 Stats: STR, DEX, CON, IQ, LK, CHA, SPD, POW. 3d6 TARO each
7.X Stats: STR, DEX, CON, SPD, INT, CHA, LK, WIZ. 3d6 TARO each
TARO: Tripples Are Roll Over (and add)... an open ending process.

Types (aka Classes)
5.x: Warrior, Wizard, Rogue, Warrior-Wizard*, (Monster)
7.x: Warrior, Wizard, Rogue, Paragon*, Citizen, Specialist Wizard (4 subtypes), Specialist-Ranger, Specialist-Leader, (Monster)
*same type, different name
Monster is mentioned as a non-type, but applies to certain monsters.
Warriors double armor worn, never cast magic
Wizards use staves to reduce magic costs. 2d max weapon.
Specialist Wizard: 1/4 the spell list available, but known automatically. 2d max weapon.
Ranger: all rolls to hit with missile weapons are level 1.
Leader: all rolls to influence NPC's are level 1.
Citizens: adds halved, casting sucks
Rogue, 5.x: cast spells, normal adds, no weapon restrictions
Rogue, 7.x: roguery talent and as 5.x. Roguery may be used in place of any INT, CHA, or LK test, and uses the one picked at creation as its base.

Skills:
5.0: None
5.5: Slots=IQ, buy +1 to att for 1-3 slots, cost by which skill. New slots as IQ raises
7.0: Talent starts 1d6 over attribute when aquired. Each +1 to base attribute is +CharacterLevel to talent. 1 talent at creation, +1 per character level gained.
7.5: Talent level is 1d6. Talent adds to stat when applicable. 1 talent at creation, +1 talent per character level gained.

Levels and Advancement Points
5.0, 5.5: AP totaled, compared to level chart. When sufficient gained, add level # to one attribute of choice (LK gets double level).
7.0: AP spent to raise attributes individually. +1 Attribute is Current Stat x 100 AP. Level is based on highest of your type's level attributes; that attribute/10, round down, is character level.
7.5: AP spent to raise attributes individually. +1 Attribute is Current Stat x 10 AP. Level works same as 7.0
All: AP Gains are equal to MR defeated, or Attribute total defeated, or SR Level * actual roll on the dice.

Magic
5.0 Magic spends STR, which is recovered 1 point per 10 minutes. Spells have minimum DX and IQ to learn it by any means. You can only buy spells if a wizard and of same or higher character level as the spell, but rogues and wizards can learn spells from other characters by other means. No casting checks; spent the ST, it goes off. ST Cost raised if spell above your level, lowered if below, lowered if a staff is used.
5.5 as 5.0, but spend POW instead.
7.x: Spells have a DX and INT requirement; if you meet that, then you can learn it. Casting spends WIZ, recovered 1 per 10 minutes. Wizards can only buy spells they can learn; specialist wizards automatically know any spell they can use. To cast, wizards, rogues, paragons and specialist wizards make a Save on IQ to cast and spend WIZ. Citizens make both a DEX and INT save. Casting difficulty is spell level. If caster's current WIZ less than target's current WIZ, spell fails, but reduces target's WIZ by the casting cost; may abort before even making rolls to cast. Cost reduced by amount Character level exceeds spell level, but not increased if spell level higher; cost reduced by staff.

Combat: pretty much the same across the board. 5.5 and 7.X add "Spite Damage"; each 6 rolled is 1 point minimum past armor; in 5.5, the loser alone does spite. In 7.X, both note it, and monsters may spend spite instead on other special effects.

Saving Rolls:
All
2d6 Doubles are Roll Over (and add), minimum natural roll 5+ after DARO, for a 4/36 minimum chance of fail, for a TN of 15+(5xDifficulty Level)-Stat. (In 5.5 and 7.5, talent or skill adds to stat for this purpose; in 7.0, talent replaces stat, but talent will always be higher anyway).
in 5.5 and 7.X, failure by less than character level may be converted to a success; in 5.5, it's implied that this should be a partial success, while in 7.0, it isn't.

Combat adds:
5.x: melee based on ST, DX, LK; Missile ST, DX, DX, LK (yes, DX counts double!)
7.x: combat adds based on ST, DX, LK, SPD.
7.5: Warriors get to add Character Level to Adds.


In general: character levels are lower in 7.X, but advancement is more smooth, and often more even.
5.X, higher character levels, but lower stat totals, and often wildly imbalanced due to advancement system.

7.x, due to the having to have a higher wiz than target, gives warriors a reason to raise WIZ; in 5.5, POW was a "dump-stat".

7.x is missing the languages tables/rules

note that both 5.5 and 7.5 are in print, 7.0 and 7.5 are available as PDFs (FDP and DTRPG, respectively). "M6" is ALSO in print, and I don't have it, but it does advancement and AP gains differently.

Characters from any work in adventures from any, tho'... but you may need to fake WIZ for some combats. Roll it for Warriors & non-spell-using monsters; set it equal to ST for Wizards.

Wow. That is a pretty thorough comparison. Much obliged. If you had to choose one, which would it be?

Well, I certainly can't add much to what Aramis already covered insofar as differences.

I think they're both good games, though I prefer 5th for being a lil bit less fiddly. (I don't dig the Kremm Resistance and the change in experience advancement in 7.x)
There's some good ideas in 7.x that I use, but then again, most of those had long been popular house rules for 5th ed. anyhow.

One thing 5th does have on 7.x is that it generally goes into a bit more depth and 'covers more ground' than the recent iteration seems to.
You really can't go wrong with either, however.

It may be worth noting presentation if such things matter to you. 7.x is available only as part of a package deal. Also, it's a small digest-sized, spiral-bound book. Whereas 5th ed. is a standard-sized, perfect-bound book and can be had in either a box set or the rulebook alone.

I think I'm leaning towards the older boxed set. I'm just feeling a bit nostalgic after working on my Red Box tribute game.

5th ed has Liz Danforth's art which to me was always a big part of T&T. I also think the writing in 5th is stronger. Hard for me to be objective 5th ed was the first RPG I played and I still think it's a great game. I didn't think 7th ed added much to be honest.

If you are unfamiliar with T&T in general, 5.5. But note that it's 5.0 plus an upgrade section, rather than a revised 5.0 rulebook.

5.0 has Liz Danforth's wonderful editing, & she Translated Ken-speak to English... Her art is good, but her editing made the game easily digested.

7.5 is, however, what I am running. We've been down a few weeks (swine flu outbreak, I had an infected toe, Sherrie, the host, was exhausted from new job, etc.).

BTW, 7.x prints nicely readable 4-up on LTR paper... Print out double sided, and page protectors, then into a report cover... very nice rulebook. Or booklet print it to LTR, and get a digest sized book. You'll need to use a heavy stapler, tho, like an Arrow T50 Construction staple gun.

It also reads VERY nicely on a Sony PRS-500/505/600/700 screen. (Not on the Kindle, tho, since the kindle don't do PDF directly.)

I'll get the printed version. 5 is still my choice right now. Thanks.