That really is a HUGE question to try to answer, and, really, a lot more info from you is needed!

Summer - June through to mid-September, say - is VERY hot. This year it ran at a high of over 105 F every day for almost 5 weeks. Even now, it has been 103 there today. The heat however is different from, say, Florida - it's much less humid.

Spring is good, as is Autumn. Watch out for conventions descending on LV as these swamp the hotels sometimes.

As to where to stay, they have everything from top-end super luxury to cheapy cheapy basic hotels. All depends what you like.

Read the forum - especially from poeple posting trip reports on their Vegas experiences (there's a couple of very good ones quite recently)

Totally depends on what you want to do whilst you're there. If you want to chill out around a pool by day and enjoy the entertainment at night, then May, September or October is a good time to go. If you don't want to sunbathe at all and just want to sightsee then March/April/October/November is really comfortable.
As Sancho said, it's always worth Googling Las Vegas conventions to make sure you avoid any big ones in town as hotel prices will go up and it can get busy. Sometimes you can get decent flight deals in January when some companies have new year sales, Virgin and Expedia both often have sales in January.
Have a read of the trip reports and Vegas threads on here to get more info, there's been a few of them and they should give you a good idea of what's available and of things to do/see.

Cheers,

TC

Yes, defintely would need to know whether your plans include enjoying the sun and pool or not. And maybe also what months you would holiday in Spain for example....personally I wouldn't go to Spain etc in July as it's too hot, so July and August in Vegas are a no-no for me.

Just back from a September trip, we tend always to go in September, partly because it's my birthday but also the weather is pretty much guaranteed, albeit a little too hot. It is very pleasant in the evening though, I like it warm at night, we often go outside the casino for a heat!

As TeeCee says the start and end of summer good for sunbathing, spring, autumn good if you just want comfortable walking weather but not quite pool weather. Or if you don't care about weather just look for a cheap flight when there's no conventions on. December before xmas is particularly cheap for hotels, as is mid-summer when it's very hot.

Lots of help available on here, so read away then ask us more questions!

thanks for the replies am looking to wander around do helicopter rides and see as much as possible in 5/6 days so don't want it too hot.
will have to keep looking

I am thinking then April or May or October sound best.

It can be really hot, like being in an oven! It's a dry heat, but it's still uncomfortable and very easy to get dehydrated if you're out walking.

We went mid July, and to be honest it was to hot to take full advantage.

We like to have a good hike about and the heat both day and night severely limited this.