That depends on what you like. Enfields, for example, are very low on my list. I don't like shooting them (many left handed shooters find the bolt akward). If I can't shoot it (even if it is a safe queen) I don't want it.
I have started a collection of South American Mausers. It is one rifle strong at the moment. But any and all variants will become must haves for me. And many will be difficult if not impossible to find in any condition.
Ask yourself a few questions:
1. Do you plan to shoot you collection?
2. Can you reload? Do you like to reload?
3. How much are you willing to spend on a firearm? (gun, accessories, dies, brass, surplus ammo...)
4. Do I have limited space to store them?
Reasons for these questions:
1. If so, ammo costs and avalability become issues as might replacement parts.
2. If you don't want to reload to shoot, figure in expensive ammo for some guns, or maybe even not shooting them.
3. Don't buy a Steyr m95 because it's cheap if you want to shoot it. Surplus ammo for that is almost dried up, so you will be reloading for it, and the components aren't standard so it costs more than reloading for other rifles.
4. Don't fill your safe with cheap mosins or yugo mausers and then pass up on rare gun deals due to a lack of space. Either plan on more safes, or storage room, or make up a list of must haves and then stick to it so that you don't have to lament missed dream guns.
Hope this helps.
(My answers are)
1. Yes, see above.
2. I reload.
3. That is personal but is part of why my collection is what it is.
4. Out of room at the moment, but a new cabinet will be ordered eventually.