Should I purchase a 18-55mm or 55-250mm lens?

I have just purchased a Canon 7D after selling a entry-level Nikon and need to purchase a lens which will be primarily used during an overseas trip to Europe. Due to my limited budget I'm currently looking at the EF-S 18-55mm f/3.5-5.6 IS II or Canon EF-S 55-250mm F4-5.6 IS II Telephoto Lens.

I know the benefits/advantages of both but was more asking based on others experiences to see which lens you personally found more useful or of better quality.

One has to wonder why you switched camera systems. Usually when people do this, they have a few years experience using the first system and usually move to the other one based upon sensor performance.

In any case, they would have enough experience know what lenses they need to replace.

If you had a Nikon D5200 with a 18-55 mm and 55-200 mm lens, then this question would seem to be redundant.

You certainly would know that the 18-55 mm lens can cover landscapes, groups, full body shots and head and shoulder shots. Probably the most useful of the two as someone begins to learn the fundamentals of photography.

A Canon 55-250 mm lens would be one used if you wanted to get more reach like when shooting field sports and some wildlife, but not very convenient for shooting the standard shots people tend to shoot when traveling. For that reason, I always suggest starting with the 18-55 mm lens and use it for a few years before you decide which next lens you want or need.

When traveling in Europe, the lens I would take if I had a Canon System, would be the 10-18 mm super wide angle lens. When I travel, the most used lens is my Nikkor 12-24 mm lens followed by a Nikkor 24-70 mm f/2.8

I don't want to rain on your parade, since I'm sure you have your very good reasons for switching from Nikon to Canon system, however I will leave you with these two links.

I'm a sports photographer and about six years ago, many of my colleagues moved from Canon to Nikon when the Nikon D3 was introduced with its amazing low light performance. Now with the introduction of the Nikon D810, some of the holdouts are now making that move.

Since the cost of switching camera systems can be rather expensive (especially if you are a pro and are replacing your $6,000 plus camera bodies and usually around $25,000 in lenses and other accessories), there has to be a very compelling reason to make such a change.

I use the 18-55mm and 50-200mm Pentax K-mount lenses regularly. I would never buy the 50-200 first. 18-55mm is much more versatile, and that's the one I carry all the time.
If you wanted to jump into, say, sports photography, you could think about the 50-200, and use a point and shoot for more regular shots.

The lens I find useful when traveling is my Tamron 18-270mm PZD lens. I've never needed anything wider, so I would choose the 18-55mm for you. If you could stretch your budget to get the 18-135mm, that would be good.
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I would not recommend a superzoom, because 18 MP is going to magnify its deficiencies. An EF-S 15-85mm IS could be a good choice, but it may not fit your budget. The EF-S 18-135mm STM is reputed to be sharp, but it has some chromatic aberration. If you would have bought a 70D it could do processor correction for that, but the older 7D won't. It could have been bought less expensively in a bundle with the 70D, but you went and bought a &D body instead.
So I think it is the EF-S 18-55mm IS for you.
On the bright side, if you have plans to hit your camera with a bus or set it on fire, the Canon 7D is a good choice.

You have so yea basicaly some potato

It depends on what you will be photographing mainly.
If it's landscapes and scenery, the the 18 - 55 is best.
But if you intend to shoot far away details in, say buildings or scenery, then the longer lens is better.

Technically your need both lenses and probably a lot more as you get into different types of photography like portraits and macro, just to name a couple. That is the "lot" of DSLR's. Most DSLR's come with a 18-55mm, we call the "normal" zoom range. But you want to pull in more distant scenes/object you need more telephoto or a 50-200 or 55-250mm lens. Do not buy just a body of a name brand as these are designed for the person who needs two camera bodies but does not need two 18-55mm lenses.
Asking this type of question says you really should proceed slowly in making you decision to purchase a DSLR tyep in the first place. Perhaps a good "bridge" camera that uses one zoom lens to do everything from wide angle to telephoto to macro, shots.