A lot depends on what you want to do in terms of accuracy and quality.
However, of all the sig gens mentioned on here the little Marconi 2022 is likely to be the best choice for most people for small business/hobby use. However, they are not always that reliable because they have a known weakness in the (many) OM345 modules inside the unit. But these are relatively easy to repair/replace and there is very little else in the way of unobtanium inside the generator.
The Mi2022 is small, easy to use and has reasonable phase noise performance. We have loads and loads of them at work (at least 10) and I don't think any have had an OM345 failure in the many years we have had them.
The main problem with the HP sig gens mentioned on here is the size and weight. I don't rate the HP8657 series as worth the bench space because the size/cost/performance/'ease of repair' ratio doesn't add up for me. The performance is fairly average but the generator is big and heavy.
The HP8640 is a classic signal generator with fantastic spectral purity but for most modern users it will be too big, way too heavy and old and slow/clunky and fragile. The Marconi 2017 is a decent competitor/alternative to the HP8640 with a much, MUCH better user interface but it is incredibly heavy and I wouldn't recommend it unless you want diehard spectral purity and you can live with the size/weight/power requirements.
The Marconi 2019(A) is fairly common as a used buy in the UK for maybe £150 -£300 but I would advise against these unless you are prepared to put up with lots of niggly/intermittent reliability. This is fine if you like taking things apart and fixing minor faults but not good if you want decent long term reliability. They are much bigger/heavier than the 2022. I have two of them here and they are nice to use but they are big and heavy and the attenuators can stick/misbehave if the instrument does not see regular use. But most of the modules inside use discrete, easy to find components so repairs can often be very cheap and quick.
The other bonus with the 2019 is that it is totally SILENT in operation because there are no fans anywhere. So if you like to work in silence and hate fan noise then the 2019 can become top choice if you have the necessary bench space and get one that is reliable. The phase noise performance of the 2019 is fairly poor above about 300MHz but it gets better at lower frequencies because of the way it uses dividers for the lower bands. So it is quite respectable for close to carrier phase noise across 2-30MHz.
This makes it a good (but not spectacular) choice for use in this range of frequencies.
There's a very good reason why the little 2022 holds its (£200-£400) price so well. It is in a class of its own in terms of size/weight/performance/ease of repair and this makes it a very popular choice for hobby users
Ebay has its fair share of sellers trying to get very high prices for the 2022 (eg >£800) but I think you can often get them for under £300.
If you do go for a 2022 then it's worth asking the seller if the generator works on all its sub ranges. Even though it appears to be a seamless interface to 1GHz the generator can have known dead 'gaps' in this frequency range if it is faulty. eg it can work perfectly well in parts of its range but be dead on others. Usually it means a dead OM345 module somewhere.
There are various options if an OM345 fails. You can try and buy an OEM version (£30 each?) or buy a dodgy 'equivalent' on ebay for about half this amount or you can try and repair the OM345 yourself (at zero cost)