Before I get started, I want to say that I enjoy crunching numbers, so this is a bit long winded. Therefore, I have broken it down into a few headings.
Really, this is entirely up to you. Just for general knowledge, you will get 6500 gp for every point if you choose the cash. Alternatively, you can get 25 times the number of points you have, times your level in a skill if you choose the exp.
So, with the five points you have, you can get 32.5k, or experience in a skill. If you really want to, you could work out how much training a particular skill would cost (we'll use construction as an example). If the cost of training is lower than that of the amount of cash that you would get, and assuming time is not an issue, then the cash reward would be ideal. If the cost of training is higher, then go for the exp.
Here's a small example Edit
Let's say you had level 33 construction (for oak larders) Oak planks = 60 exp each, 435 GE price
With 5 penguin points, you would get 33*25*5 exp = 4125 exp Dividing by the number of oak planks, and multiplying by the price per plank, that it would take to train this normally would be 30,015gp
Alternatively, you could get 6500 gp *5 = 32500 gp
Summary of Example Edit
So, your first option is getting the cash reward (32500 gp) and spending 30,015 gp on construction to get 4125 exp. This would mean that you get an extra 2485 gp.
Your second option is to essentially "purchase" 4125 exp in construction for a 32500 gp.
So, if you look at the math, you can see that the cash reward would be worth it for training a skill that is low. The exp reward would be worth it for skills that are already high or that cannot be "bought."
What I have spent points on Edit
- Construction: this skill takes a good bit of cash, so if you have it at a high level, spend the points on exp.
- Herblore: unless you are really into farming or killing chaos druids, this will also be very expensive.
- Summoning: Again, this skill can be very expensive to get large amounts of exp.
- Agility: A very time intensive skill, but one with many advantages to have at a high level.
- Farming: Also fairly time intensive. Unless you want very slow exp, it is often also fairly expensive (Personally, I spend points on this most of the time as it is also one of my lower skills)
- Slayer: Very slow to level up and very profitable at higher levels (Personally, I will probably spend points on this after I level farming a bit)
- Runecrafting: Again, very slow to level up, but very profitable at high levels. The exp from penguins can be a nice boost to it