Are there any Dell or other laptop experts here?

I've traded used gear all my life. between the early nineties and mid 2000's I traded computers and did company clearances.

All that knowledge is now irrelevant, but I have a certain amount of skill at "choosing good hardware"

After a cursory glance I decided I liked item 3. I don't know why... I didn't like item 1.

All were available much cheaper from private sellers. I like private sellers because they have used the machine for a while unlike a dealer, who has put it though a "refurb loop" which does not do much to add reliability. 

I don't know if any of that is helpful at all, I feel I ought to be able to add more... Dell, HP and on a good day Toshiba. I've never done well with IBM/lenovo. Most of the other makes fall apart too quick, and, Sony?Just say NO.

*Edit* as a small trader with limited spares access, I always prized, "will it work as the customer expects for the next year or two," over "features", "bling" or "specs"..

So am I right, if a Dell has a higher number, does that mean it's a newer model? e.g. a 6430 would be newer than a 5550?

I was favouring item 2 (the 3550) but then realised that is older than my 5558 I've had from new. So maybe I will change over to the 6430u. Is that the one you favoured? The Latitude I've got is 5540. So going for a 3000 series wouldn't make sense would it.

You have to give me reasons for why you liked your choice though, you can't just say you don't know why. *shakes fist at you*  

So am I right, if a Dell has a higher number, does that mean it's a newer model? e.g. a 6430 would be newer than a 5550?

I was favouring item 2 (the 3550) but then realised that is older than my 5558 I've had from new. So maybe I will change over to the 6430u. Is that the one you favoured? The Latitude I've got is 5540. So going for a 3000 series wouldn't make sense would it.

You have to give me reasons for why you liked your choice though, you can't just say you don't know why. *shakes fist at you*  

Let's see what other people say, because we 'spergs do end up in I.T. quite often, 

Yes that's why I asked, I hoped to get some experts.

Thanks, I found out the number doesn't mean the higher Dells are newer, I looked on Wikipedia for that, hopefully it's right. I did like the look of the 3550 originally but the 6430 seemed newer due to the number but maybe it's not.

It's between the two Latitudes for me, I'll think about it more and decide. I've already got a Latitude and it's great so I want another. My Inspiron is so old it's on its last legs I think...

IIRC, when I did a lot of Dell, they split their machines into lattitude which were a more staid tried adn tested platform aimed at the business user and inspiron which tended to be aimed ta the home user and a bit more "experimental". I.E. if it works well in last years inspiron it'll appear in this years latititude, possibly done a bit better. Then IIRC correctly "alienware" is the cutting edge stuff made for gamers and Sheldon Cooper.

I looked at your specs, which were all fairly similar, then briefly browsed the machines on ebay, and found I liked the "look" of the three machines you specified in ascending order. 

I did not give your request the attention I'd give it if you were my daughter, for example, but I'd be surprised if even after "getting into it properly" if I'd choose differently. I've normally got a good thing going for buying used hardware.

Personally I'd probably buy laptop Number 2 if the price difference is as great as appeared after a quick glance, but IIRC, I saw 2 off laptop number 3 being offered for 99 quid, somewhat incomplete, but I'd be taking a long hard look at that.

I'm trialling my first SSD laptop right now, A lenovo that I won for being in the right place, at the right time, working for the right people and I've already busted the screen cable by moving it too much (which I've never doesn't before with any other make of laptop AFAIK) and I'd feel happier if I had a regular backup thing going, I suspect that when an SSD fails, it may fail totally, all at once.

Unfortunately my mate sold his I.T. Disposals company some years back, otherwise I could get the "skinny" on this quite quickly. 

Let's see what other people say, because we 'spergs do end up in I.T. quite often, I.T. people love to "one-up" one another, and this discussion sets the stage nicely. I was hoping someone would have showed up already to tell me why option 3 was either not the best, or to offer an "option 4"...